Gaps in measles immunisation coverage for pre-school children in Aotearoa New Zealand: a cross-sectional study
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Measles is a highly contagious disease resulting from measles virus infection. Since the implementation of measles vaccines in the 1960s, incidence of measles and associated mortality have been largely reduced. Nevertheless, the global number of deaths that were attributed to measles was estimated to be over 140,000 in 2018, mainly occurring in low-income countries in Africa and Asia.[[1,2]] In particular, unvaccinated children under 5 years of age are at high risk for measles-related complications leading to hospital admission or even death.
Aotearoa New Zealand has notable immunity gaps in the population and the measles immunisation coverage target of ≥95% to prevent measles transmission has not yet been reached. Over the last few decades, following improvements in the national immunisation programme, immunisation coverage has increased (fully immunised at 2 years: 56% in 1992 to 91% in 2019).[[3,4]] For the birth cohorts of 1980–1999, the historically mediocre coverage rates have created an immunity gap due to insufficient measles immunity. Although catch-up immunisations have been offered, the immunisation coverage numbers for the birth cohorts of 1980–1999 are unclear.[[5,6]] Furthermore, in 2020 and 2021 New Zealand immunisation coverage rates have decreased relative to previous years (fully immunised at 2 years: 76% in 2020 and 85% in 2021), likely partly due to disrupted routine immunisation programmes early in the COVID-19 pandemic—a development that was also observed in other countries.[[7–11]] In addition, important differences in immunisation coverage exist between ethnicity groups, with lower coverage in Māori and Pacific peoples.
In 2017, New Zealand received a measles-free status following the absence of local transmission in the previous 3 years. Recent outbreaks in New Zealand have been linked to imported cases, and since a large outbreak in 2019 there have been no measles notifications.[[12]] Importantly, New Zealand is connected with the Pacific Islands and frequent travel across the Pacific occurs. Following the New Zealand measles outbreak in 2019, measles then spread to Samoa and caused a great impact with 83 deaths in a population of 200,874, of which 87% occurred in children <5 years.[[13]]
Since April 2022, measles outbreaks have been globally reported and have mainly occurred in Africa and the East Mediterranean region.[[14]] In July 2022, the New Zealand borders fully opened and, together with increasing measles cases worldwide, the likelihood of imported measles cases has increased. Identification of immunity gaps is important to specifically target public health resources. Therefore, in this study we aimed to describe gaps in immunisation coverage by ethnicity, socio-economic deprivation and region for measles in New Zealand children under 5 years of age.
Methods
Study design and the New Zealand measles immunisation programme
This was a cross-sectional study using publicly available data from the National Immunisation Register (NIR).[[7]] This study is exempt of ethics review as the study involved analysis of publicly available data that do not contain any sensitive health information. The data is held and curated by the New Zealand Ministry of Health.
The NIR records immunisation details for children born since 2005. Since 1 October 2020, the New Zealand immunisation schedule recommends that children to receive the first measles, mumps and rubella (MMR1) vaccine at 12 months (circa 95% seroconversion), and the second MMR (MMR2) vaccine at 15 months (circa 99% seroconversion). Prior to 1 October 2020, MMR dose one was administered at 15 months of age and MMR dose two was administered at 4 years of age. Following the measles outbreak in 2019, a measles immunisation campaign was implemented to improve immunisation rates. Activities for this campaign included maximising the uptake of MMR at 15 months and at 4 years with an active recall for children <5 years who had missed either of these two doses, and an MMR 0 dose for babies from 6–11 months old in the Auckland region.
Data collection
We extracted measles coverage rates for the MMR1 vaccine and the MMR2 vaccine for birth cohorts 2017 through 2020 on 22 June 2022. In these cohorts, all included children were offered MMR1. The MMR2 coverage rates, however, were influenced by the programme change in October 2020. Therefore, children who received MMR1 on time at 15 months may not have been offered a second dose before 4 years of age. Stratified data were extracted by prioritised ethnic group, by district health board (DHB) and by socio-economic deprivation quintile (1 to 5) defined by the New Zealand Deprivation Index 2018 (NZDep2018).[[15]] Deprivation quintile 1 represents areas with the least deprived scores, whereas deprivation quintile 5 represent areas with the most deprived scores. Though DHBs no longer exist as of mid-2022, for ease of interpretation and consistency with historical data, we retain the DHBs. We assessed population density using data from Statistics New Zealand. In addition, we collected data from previous measles outbreaks from the New Zealand Ministry of Health.
Data analysis
Firstly, we described MMR1 and MMR2 coverage rate, and whether the immunisation coverage rate was ≥90%. Although we planned a description of the MMR coverage target of ≥95%, we chose the 90% cut-off as none of the birth cohorts reached the 95% cut-off for MMR2. We combined data for the 2017–2020 birth cohorts, and also presented data for each birth cohort separately. Secondly, we stratified for ethnicity groups and per deprivation quintile. Thirdly, we illustrated MMR1 and MMR2 coverage per DHB using geographical heatmaps. Since DHBs comprise large areas and population density is a risk factor for a future measles outbreak, we performed a sub-group analysis of the 10 Territorial Authorities with the highest population density (Appendix 1). Next, since the Auckland region has the largest population, we performed a more detailed geographic analysis using coverage rates per the 2013 Area Unit (AU). In an urban setting such as Auckland, an AU is generally a collection of city blocks. Lastly, we described the DHBs with highest case and hospitalisation counts in the 2019 measles outbreak.[[16]] Children with missing data on deprivation quintile (<1%) or whose DHBs were classified “undefined or overseas” (<1%) were excluded from stratified analysis. All analyses were performed in R version 4.2.
Results
Overall MMR coverage
Overall, the coverage for MMR1 was 92.5% and the coverage for MMR2 was 74.6% for children born between 2017 and 2020. The coverage for MMR1 declined from 95.1% for those born in 2017 to 88.9% for those born in 2020 (Figure 1a). The coverage for MMR2 was below 90% for the studied birth cohorts: the lowest MMR2 coverage was observed for the birth cohort of 2018 (61.6%). MMR2 coverage increased for those born in 2019 (72.8%) and in 2020 (80.3%).
View Figures 1–3 and Table 1.
MMR coverage per ethnicity
Coverage for MMR1 was above 90% in all birth cohorts for children of Asian ethnicity (range 97.6% to 98.4%), NZ European ethnicity (range 91.7% to 94.8%) and children of other ethnicity (range 90.1% to 93.7%) (Figure 1a). MMR1 coverage was lowest for children of Māori ethnicity and coverage declined over time: from 92.8% for the 2017 birth cohort to 78.4% for the 2020 birth cohort. For Pacific children MMR1 coverage was above 90% for those born in 2017 to 2019 (range 92.3% to 97.0%) but was 88.3% for those born in 2020.
MMR2 coverage was <90% for all birth cohorts in each ethnic group, with the exception of children of Asian ethnicity in the birth cohorts of 2017 and 2020 (Figure 1b). For all the ethnicity groups, MMR2 coverage was lowest for the 2018 cohort (NZ European 66.1%; Māori 48.4%; Pacific 55.5%; Asian 72.7%; Other 63.6%). MMR2 coverage increased for all the ethnicities in the birth cohorts of 2019 and 2020, although coverage has not yet reached the 2017 level for children of Māori, Pacific and NZ European ethnicities.
MMR coverage per socio-economic deprivation quintile
MMR1 and MMR2 coverage was lower in the more socio-economically deprived areas compared to less deprived areas (Appendix 3). The difference of MMR1 coverage between the least deprived areas and the most deprived areas increased from 1.7% in birth cohort 2017 to 9.2% in birth cohort 2020. The difference of MMR2 coverage between the least deprived areas and the most deprived areas ranged from 12.5% (birth cohort 2017) to 17.5% (birth cohort 2018), and was around 15% for birth cohorts 2019 and 2020.
MMR coverage per DHB level
Across the birth cohorts, MMR1 coverage decreased in all DHBs (Figure 2). Six DHBs had an average MMR1 coverage <90% (Bay of Plenty, Lakes, Northland, Tairāwhiti, West Coast and Whanganui). None of the DHBs had MMR2 coverage >90% (Figure 3). For the birth cohorts 2017–2020 combined, the lowest MMR2 coverage was observed in Northland (59.1%), Waikato (61.2%) and Lakes (62.1%) (Appendix 4).
MMR coverage for top 10 population density areas
The 10 areas with the highest population density are presented in Table 1. The average MMR1 coverage was below 90% for Kawerau and Tauranga. Apart from Wellington, the other areas all had MMR2 coverage <90%. Average MMR2 coverage was lowest for Hamilton (62.8%), Napier (68.9%) and Auckland (73.8%).
For all birth cohorts, coverage for Auckland was above 90% for MMR1 (range 92.3% to 96.6%) whereas coverage for MMR2 was below <90% (range 67.4% to 83.7%). MMR1 and MMR2 coverage varied across AUs for Auckland (Figure 2 and Figure 3). For the Auckland area, the number of AUs with MMR1 coverage <90% increased from 2/106 (1.9%) in birth cohort 2017 to 26/106 (24.5%) in birth cohort 2020. For almost all AUs, MMR2 coverage was <90% for those born in 2018 (101/106, 95%) and in 2019 (98/106, 92.5%).
2019 measles outbreak
In the 2019 measles outbreak the Auckland metropolitan area was most affected. The DHBs with the highest measles incidence in the 2019 outbreak included Counties Manukau (measles incidence 202 cases per 100,000; hospitalisation rate 77 cases per 100,000), Northland, Auckland and Waitematā (Appendix 5). In these DHBs, MMR1 coverage decreased across the different birth cohorts. For the 2017 and the 2018 birth cohorts combined, the MMR1 coverage was 93.2% in Counties Manukau, 84.4% in Northland, 95.1% in Auckland and 93.8% in Waitematā. For those born in 2020, MMR1 coverage was 89.2% in Counties Manukau, 77.0% in Northland, 92.2% in Auckland and 90.3% in Waitematā.
Discussion
In this cross-sectional study, we assessed measles vaccine coverage rates in young children in New Zealand. Concerningly, coverage for MMR1 has been declining, especially in Māori children. In addition, MMR1 coverage declined in all DHBs, with six DHBs having average MMR1 coverage <90% for the birth cohorts of 2017 to 2020. Immunisation coverage for measles is therefore insufficient to prevent community transmission in young children.
Globally, the World Health Organization reported that coverage of at least one dose of measles vaccine was 81% in children 2 years of age in 2020. For children in New Zealand born between 2017 and 2020, the MMR1 coverage is 92.5%, which is higher compared to the global average, and is similar to the coverage in other high-income countries (MMR1 93%).[[17]] In order to prevent measles transmission in New Zealand, the current coverage should be increased to reach the 95% target.
The heterogeneous immunity in the New Zealand population remains a risk factor for any future measles outbreak. Contributing factors to the 2019 measles outbreak included the recent decline in infant immunisation coverage in addition to the immunity gap in young adults, especially those of Māori or Pacific ethnicity.[[5]] Our study focussed on the description of immunisation coverage in young children as this group is at highest risk for measles-related complications. We acknowledge the lower immunisation coverage in young adults, who may have a key role in the importation and transmission of measles in New Zealand communities. However, these cohorts received MMR vaccines prior to the commencement of the NIR, which makes accurate estimates of coverage challenging. To address the immunity gap in young people both up-to-date immunisation records and the immunisation coverage should be improved.[[5,6]]
Hayman et al. analysed risk factors for measles up to 2014 in New Zealand, and observed that the greatest measles importation risk is during December in which a high peak of travel occurs. Likewise, measles is probably imported from regions with both high travel rates (e.g., Australia, United Kingdom) and higher measles incidence (e.g., China, Indonesia).[[18]] During the COVID-19 pandemic, the risk of importing measles had been minimised due to the New Zealand border restrictions. With the opening of the borders in July 2022, together with the recent increase of measles cases in Africa and the East Mediterranean, there is an increased risk of measles importation through international travellers. Besides the risk of importing measles to New Zealand, a measles outbreak could also influence the risk of exporting measles to Pacific islands where health systems are more fragile.
Since the start of the COVID-19 pandemic, many countries have had disruptions of their routine immunisation services. Worldwide, coverage of the first dose of the measles vaccine has fallen about 7% from 2020 compared to 2019.[[19]] In New Zealand, MMR1 coverage was already declining before 2020, along with a declining trend in coverage for all childhood immunisations that has been observed since 2015.[[20]] Our study showed that a decreasing trend for MMR1 has been observed in all DHBs, emphasising that a national programme is needed to improve immunisation coverage. In the 2019 measles outbreak, the metropolitan area of Auckland was most affected with over half of the measles cases occurring in Counties Manukau. In children born between 2017 and 2018, the combined MMR1 coverage for Counties Manukau was 93.2% This emphasises that measles immunisation coverage needs to be higher to reduce the chances of transmission. It should be noted, however, that the immunity gap in adolescents could have played a role in this outbreak. Further, the previous outbreak could have increased the immunisation coverage in this area.
Immunisation coverage for measles varied by ethnicity with highest coverage rates in Asian children and lowest coverage in Māori. Previous research has shown that the higher immunisation rates in Asian children are mainly due to the positive attitude of parents towards timely vaccination of their children.[[21]] Immunisation coverage for MMR1 decreased by approximately 15% in Māori children comparing those born in 2017 to those born in 2020. This decrease is concerning, and public health resources should focus on improving immunisation coverage in this group in order to achieve equitable health outcomes. For instance, the emergency meningococcal C vaccination programme in 2011 reached equitable and high vaccination coverage.[[22]] In this programme, vaccination was promoted via various services. Vaccination programmes should include general practice services, community outreach clinics and involvement of Māori health providers.
Ideally, measles immunisation coverage should be >95% to reduce transmission. While, ideally, coverage should be boosted for both MMR1 and MMR2 the focus should initially be on MMR1 to have the greatest impact on preventing community spread of measles. In addition, immunisation programmes should consider focussing on improving coverage for other vaccines as well. Furthermore, healthcare accessibility should be ensured, including cultural safety in health services. Besides improvement of vaccine delivery including consistent involvement of Māori and Pasifika leadership and the use of mobile vaccination clinics, parental attitudes regarding vaccine safety should be addressed using effective communication. This is especially important as about 30% of the New Zealand population has concerns regarding vaccine safety.[[23,24]]
Strengths of this study include the detailed description of MMR1 and MMR2 coverage for young New Zealand children using high-quality data from the NIR.[[25]] In addition, we provided detailed geographical analyses of areas with high population density. This study has some limitations. Firstly, we did not study children born in 2021 as not all children in this birth cohort were eligible yet for their first MMR dose at 12 months. Data showing the overall immunisation coverage confirms the ongoing decreasing trend in the 2021 birth cohort.[[7]] Secondly, our data should be interpreted in light of the MMR programme change in 2020, with the second MMR dose thereafter being given at 15 months instead of 4 years of age. Therefore, children born in 2018 and in 2019 may not have been offered MMR2 before 4 years of age. Thirdly, we acknowledge that occurrence of a potential measles outbreak is also influenced by other factors such as crowding and immunisation coverage rates at children’s day cares.
Nevertheless, we focussed our analysis on young children as this group is most vulnerable to measles-related complications or even death.
Conclusions
Immunisation coverage rates for measles are currently insufficient to prevent a potential measles outbreak in children <5 years in New Zealand. Concerningly, the coverage for MMR1 is declining in all regions and especially in tamariki Māori. As young children are at high risk for measles-related complications, we urge the implementation of catch-up immunisation programmes to improve immunisation coverage.
View Appendices.
Summary
Abstract
Aim
To evaluate gaps in measles immunisation coverage for children<5 years in Aotearoa New Zealand.
Method
In this cross-sectional study, we extracted coverage rates for the first measles, mumps and rubella (MMR1) vaccine and second MMR vaccine (MMR2) from the National Immunisation Register for birth cohorts 2017 to 2020. We described measles coverage rates per birth cohort, and stratified per district health board (DHB), ethnicity and deprivation quintile.
Results
Coverage for MMR1 declined from 95.1% for those born in 2017 to 88.9% for those born in 2020. The coverage for MMR2 was below 90% for all the birth cohorts, with the lowest MMR2 coverage in the birth cohort of 2018 (61.6%). MMR1 coverage was lowest for children of Māori ethnicity and coverage declined over time: 92.8% for those born in 2017 to 78.4% for those born in 2020. Six DHBs had average MMR1 coverage <90% including Bay of Plenty, Lakes, Northland, Tairāwhiti, West Coast and Whanganui.
Conclusion
Immunisation coverage rates for measles are insufficient to prevent a potential measles outbreak in children <5 years. Concerningly, the coverage for MMR1 is declining, especially in Māori children. Catch-up immunisation programmes are urgently needed to improve immunisation coverage.
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
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2) World Health Organization [Internet]. Measles. Cited 13 June 2022. Available from: https://www.who.int/health-topics/measles#tab=tab_1.
3) Turner N. The challenge of improving immunization coverage: the New Zealand example. Expert Rev Vaccines. 2012;11(1):9-11.
4) Nowlan M, Willing E, Turner N. Influences and policies that affect immunisation coverage-a summary review of literature. N Z Med J. 2019; 132:79-88.
5) Turner N. A measles epidemic in New Zealand: Why did this occur and how can we prevent it occurring again? N Z Med J. 2019;132(1501):79-88.
6) Reynolds G, Dias C, Thornley S, et al. Analysis of the Auckland 2014 measles outbreak indicates that adolescents and young adults could benefit from catch-up vaccination. N Z Med J. 2015;128(1422):53-62.
7) Ministry of Health – Manatū Hauora [Internet]. National and DHB immunisation data. [Updated 2022 Apr 29; cited 2022 Jun 13.] Available from: https://www.health.govt.nz/our-work/preventative-health-wellness/immunisation/immunisation-coverage/national-and-dhb-immunisation-data.
8) Lassi ZS, Naseem R, Salam RA, Siddiqui F, Das JK. The Impact of the COVID-19 Pandemic on Immunization Campaigns and Programs: A Systematic Review. Int J Environ Res Public Health. 2021;18(3):988.
9) Hoang U, de Lusignan S, Joy M, et al. National rates and disparities in childhood vaccination and vaccine-preventable disease during the COVID-19 pandemic: English sentinel network retrospective database study. Arch Dis Child. 2022;107(8):733-739.
10) DeSilva MB, Haapala J, Vazquez-Benitez G, et al. Association of the COVID-19 Pandemic With Routine Childhood Vaccination Rates and Proportion Up to Date With Vaccinations Across 8 US Health Systems in the Vaccine Safety Datalink. JAMA Pediatr. 2022;176(1):68-77.
11) World Health Organization [Internet]. Immunization coverage. [Updated 2021 Jul 15; cited 2022 Jun 13.] Available from: https://www.who.int/news-room/fact-sheets/detail/immunization-coverage.
12) Institute of Environmental Science and Research (ESR) [Internet]. Measles report. [Cited 2022 Jun 13.] Available from: https://surv.esr.cri.nz/surveillance/WeeklyMeaslesRpt.php.
13) Craig AT, Heywood AE, Worth H. Measles epidemic in Samoa and other Pacific islands. Lancet Infect Dis. 2020;20(3):273-5.
14) World Health Organization [Internet]. UNICEF and WHO warn of perfect storm of conditions for measles outbreaks, affecting children. [Cited 2022 Jun 13.] Available from: https://www.who.int/news/item/27-04-2022-unicef-and-who-warn-of--perfect-storm--of-conditions-for-measles-outbreaks--affecting-children.
15) Atkinson J, Salmond C, Crampton P. NZDep2018 Index of Deprivation, Final Research Report. Department of Public Health, University of Otago, Wellington. December 2020.
16) Ministry of Health – Manatū Hauora [Internet]. Measles and Rubella Elimination in New Zealand, 2021 - Report to the 8th Meeting of the Western Pacific Regional Verification Commission for Measles and Rubella Elimination, 2021. Wellington, New Zealand; 2021.
17) World Health Organization. Global Health Observatory - Measles-containing-vaccine first-dose (MCV1) immunization coverage among 1-year-olds. [Updated 2022; cited 2022 Aug 29.] Available from: https://www.who.int/data/gho/data/indicators/indicator-details/GHO/measles-containing-vaccine-first-dose-(mcv1)-immunization-coverage-among-1-year-olds-(-).
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19) Causey K, Fullman N, Sorensen RJD, et al. Estimating global and regional disruptions to routine childhood vaccine coverage during the COVID-19 pandemic in 2020: a modelling study. Lancet. 2021;398(10299):522-34.
20) Allen + Clarke [Internet]. Improving New Zealand’s childhood immunisation rates. Wellington; 2019. Available from: https://www.health.govt.nz/publication/improving-new-zealands-childhood-immunisation-rates.
21) Pal M, Goodyear-Smith F, Exeter D. Factors contributing to high immunisation coverage among New Zealand Asians. J Prim Health Care. 2014;6(4):304-11.
22) Mills C, Penney L. The Northland emergency meningococcal C vaccination programme. N Z Med J. 2013;126(1373):30-9.
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24) Lee CHJ, Sibley CG. Attitudes toward vaccinations are becoming more polarized in New Zealand: Findings from a longitudinal survey. EClinicalMedicine. 2020;23.
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Gaps in measles immunisation coverage for pre-school children in Aotearoa New Zealand: a cross-sectional study
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Measles is a highly contagious disease resulting from measles virus infection. Since the implementation of measles vaccines in the 1960s, incidence of measles and associated mortality have been largely reduced. Nevertheless, the global number of deaths that were attributed to measles was estimated to be over 140,000 in 2018, mainly occurring in low-income countries in Africa and Asia.[[1,2]] In particular, unvaccinated children under 5 years of age are at high risk for measles-related complications leading to hospital admission or even death.
Aotearoa New Zealand has notable immunity gaps in the population and the measles immunisation coverage target of ≥95% to prevent measles transmission has not yet been reached. Over the last few decades, following improvements in the national immunisation programme, immunisation coverage has increased (fully immunised at 2 years: 56% in 1992 to 91% in 2019).[[3,4]] For the birth cohorts of 1980–1999, the historically mediocre coverage rates have created an immunity gap due to insufficient measles immunity. Although catch-up immunisations have been offered, the immunisation coverage numbers for the birth cohorts of 1980–1999 are unclear.[[5,6]] Furthermore, in 2020 and 2021 New Zealand immunisation coverage rates have decreased relative to previous years (fully immunised at 2 years: 76% in 2020 and 85% in 2021), likely partly due to disrupted routine immunisation programmes early in the COVID-19 pandemic—a development that was also observed in other countries.[[7–11]] In addition, important differences in immunisation coverage exist between ethnicity groups, with lower coverage in Māori and Pacific peoples.
In 2017, New Zealand received a measles-free status following the absence of local transmission in the previous 3 years. Recent outbreaks in New Zealand have been linked to imported cases, and since a large outbreak in 2019 there have been no measles notifications.[[12]] Importantly, New Zealand is connected with the Pacific Islands and frequent travel across the Pacific occurs. Following the New Zealand measles outbreak in 2019, measles then spread to Samoa and caused a great impact with 83 deaths in a population of 200,874, of which 87% occurred in children <5 years.[[13]]
Since April 2022, measles outbreaks have been globally reported and have mainly occurred in Africa and the East Mediterranean region.[[14]] In July 2022, the New Zealand borders fully opened and, together with increasing measles cases worldwide, the likelihood of imported measles cases has increased. Identification of immunity gaps is important to specifically target public health resources. Therefore, in this study we aimed to describe gaps in immunisation coverage by ethnicity, socio-economic deprivation and region for measles in New Zealand children under 5 years of age.
Methods
Study design and the New Zealand measles immunisation programme
This was a cross-sectional study using publicly available data from the National Immunisation Register (NIR).[[7]] This study is exempt of ethics review as the study involved analysis of publicly available data that do not contain any sensitive health information. The data is held and curated by the New Zealand Ministry of Health.
The NIR records immunisation details for children born since 2005. Since 1 October 2020, the New Zealand immunisation schedule recommends that children to receive the first measles, mumps and rubella (MMR1) vaccine at 12 months (circa 95% seroconversion), and the second MMR (MMR2) vaccine at 15 months (circa 99% seroconversion). Prior to 1 October 2020, MMR dose one was administered at 15 months of age and MMR dose two was administered at 4 years of age. Following the measles outbreak in 2019, a measles immunisation campaign was implemented to improve immunisation rates. Activities for this campaign included maximising the uptake of MMR at 15 months and at 4 years with an active recall for children <5 years who had missed either of these two doses, and an MMR 0 dose for babies from 6–11 months old in the Auckland region.
Data collection
We extracted measles coverage rates for the MMR1 vaccine and the MMR2 vaccine for birth cohorts 2017 through 2020 on 22 June 2022. In these cohorts, all included children were offered MMR1. The MMR2 coverage rates, however, were influenced by the programme change in October 2020. Therefore, children who received MMR1 on time at 15 months may not have been offered a second dose before 4 years of age. Stratified data were extracted by prioritised ethnic group, by district health board (DHB) and by socio-economic deprivation quintile (1 to 5) defined by the New Zealand Deprivation Index 2018 (NZDep2018).[[15]] Deprivation quintile 1 represents areas with the least deprived scores, whereas deprivation quintile 5 represent areas with the most deprived scores. Though DHBs no longer exist as of mid-2022, for ease of interpretation and consistency with historical data, we retain the DHBs. We assessed population density using data from Statistics New Zealand. In addition, we collected data from previous measles outbreaks from the New Zealand Ministry of Health.
Data analysis
Firstly, we described MMR1 and MMR2 coverage rate, and whether the immunisation coverage rate was ≥90%. Although we planned a description of the MMR coverage target of ≥95%, we chose the 90% cut-off as none of the birth cohorts reached the 95% cut-off for MMR2. We combined data for the 2017–2020 birth cohorts, and also presented data for each birth cohort separately. Secondly, we stratified for ethnicity groups and per deprivation quintile. Thirdly, we illustrated MMR1 and MMR2 coverage per DHB using geographical heatmaps. Since DHBs comprise large areas and population density is a risk factor for a future measles outbreak, we performed a sub-group analysis of the 10 Territorial Authorities with the highest population density (Appendix 1). Next, since the Auckland region has the largest population, we performed a more detailed geographic analysis using coverage rates per the 2013 Area Unit (AU). In an urban setting such as Auckland, an AU is generally a collection of city blocks. Lastly, we described the DHBs with highest case and hospitalisation counts in the 2019 measles outbreak.[[16]] Children with missing data on deprivation quintile (<1%) or whose DHBs were classified “undefined or overseas” (<1%) were excluded from stratified analysis. All analyses were performed in R version 4.2.
Results
Overall MMR coverage
Overall, the coverage for MMR1 was 92.5% and the coverage for MMR2 was 74.6% for children born between 2017 and 2020. The coverage for MMR1 declined from 95.1% for those born in 2017 to 88.9% for those born in 2020 (Figure 1a). The coverage for MMR2 was below 90% for the studied birth cohorts: the lowest MMR2 coverage was observed for the birth cohort of 2018 (61.6%). MMR2 coverage increased for those born in 2019 (72.8%) and in 2020 (80.3%).
View Figures 1–3 and Table 1.
MMR coverage per ethnicity
Coverage for MMR1 was above 90% in all birth cohorts for children of Asian ethnicity (range 97.6% to 98.4%), NZ European ethnicity (range 91.7% to 94.8%) and children of other ethnicity (range 90.1% to 93.7%) (Figure 1a). MMR1 coverage was lowest for children of Māori ethnicity and coverage declined over time: from 92.8% for the 2017 birth cohort to 78.4% for the 2020 birth cohort. For Pacific children MMR1 coverage was above 90% for those born in 2017 to 2019 (range 92.3% to 97.0%) but was 88.3% for those born in 2020.
MMR2 coverage was <90% for all birth cohorts in each ethnic group, with the exception of children of Asian ethnicity in the birth cohorts of 2017 and 2020 (Figure 1b). For all the ethnicity groups, MMR2 coverage was lowest for the 2018 cohort (NZ European 66.1%; Māori 48.4%; Pacific 55.5%; Asian 72.7%; Other 63.6%). MMR2 coverage increased for all the ethnicities in the birth cohorts of 2019 and 2020, although coverage has not yet reached the 2017 level for children of Māori, Pacific and NZ European ethnicities.
MMR coverage per socio-economic deprivation quintile
MMR1 and MMR2 coverage was lower in the more socio-economically deprived areas compared to less deprived areas (Appendix 3). The difference of MMR1 coverage between the least deprived areas and the most deprived areas increased from 1.7% in birth cohort 2017 to 9.2% in birth cohort 2020. The difference of MMR2 coverage between the least deprived areas and the most deprived areas ranged from 12.5% (birth cohort 2017) to 17.5% (birth cohort 2018), and was around 15% for birth cohorts 2019 and 2020.
MMR coverage per DHB level
Across the birth cohorts, MMR1 coverage decreased in all DHBs (Figure 2). Six DHBs had an average MMR1 coverage <90% (Bay of Plenty, Lakes, Northland, Tairāwhiti, West Coast and Whanganui). None of the DHBs had MMR2 coverage >90% (Figure 3). For the birth cohorts 2017–2020 combined, the lowest MMR2 coverage was observed in Northland (59.1%), Waikato (61.2%) and Lakes (62.1%) (Appendix 4).
MMR coverage for top 10 population density areas
The 10 areas with the highest population density are presented in Table 1. The average MMR1 coverage was below 90% for Kawerau and Tauranga. Apart from Wellington, the other areas all had MMR2 coverage <90%. Average MMR2 coverage was lowest for Hamilton (62.8%), Napier (68.9%) and Auckland (73.8%).
For all birth cohorts, coverage for Auckland was above 90% for MMR1 (range 92.3% to 96.6%) whereas coverage for MMR2 was below <90% (range 67.4% to 83.7%). MMR1 and MMR2 coverage varied across AUs for Auckland (Figure 2 and Figure 3). For the Auckland area, the number of AUs with MMR1 coverage <90% increased from 2/106 (1.9%) in birth cohort 2017 to 26/106 (24.5%) in birth cohort 2020. For almost all AUs, MMR2 coverage was <90% for those born in 2018 (101/106, 95%) and in 2019 (98/106, 92.5%).
2019 measles outbreak
In the 2019 measles outbreak the Auckland metropolitan area was most affected. The DHBs with the highest measles incidence in the 2019 outbreak included Counties Manukau (measles incidence 202 cases per 100,000; hospitalisation rate 77 cases per 100,000), Northland, Auckland and Waitematā (Appendix 5). In these DHBs, MMR1 coverage decreased across the different birth cohorts. For the 2017 and the 2018 birth cohorts combined, the MMR1 coverage was 93.2% in Counties Manukau, 84.4% in Northland, 95.1% in Auckland and 93.8% in Waitematā. For those born in 2020, MMR1 coverage was 89.2% in Counties Manukau, 77.0% in Northland, 92.2% in Auckland and 90.3% in Waitematā.
Discussion
In this cross-sectional study, we assessed measles vaccine coverage rates in young children in New Zealand. Concerningly, coverage for MMR1 has been declining, especially in Māori children. In addition, MMR1 coverage declined in all DHBs, with six DHBs having average MMR1 coverage <90% for the birth cohorts of 2017 to 2020. Immunisation coverage for measles is therefore insufficient to prevent community transmission in young children.
Globally, the World Health Organization reported that coverage of at least one dose of measles vaccine was 81% in children 2 years of age in 2020. For children in New Zealand born between 2017 and 2020, the MMR1 coverage is 92.5%, which is higher compared to the global average, and is similar to the coverage in other high-income countries (MMR1 93%).[[17]] In order to prevent measles transmission in New Zealand, the current coverage should be increased to reach the 95% target.
The heterogeneous immunity in the New Zealand population remains a risk factor for any future measles outbreak. Contributing factors to the 2019 measles outbreak included the recent decline in infant immunisation coverage in addition to the immunity gap in young adults, especially those of Māori or Pacific ethnicity.[[5]] Our study focussed on the description of immunisation coverage in young children as this group is at highest risk for measles-related complications. We acknowledge the lower immunisation coverage in young adults, who may have a key role in the importation and transmission of measles in New Zealand communities. However, these cohorts received MMR vaccines prior to the commencement of the NIR, which makes accurate estimates of coverage challenging. To address the immunity gap in young people both up-to-date immunisation records and the immunisation coverage should be improved.[[5,6]]
Hayman et al. analysed risk factors for measles up to 2014 in New Zealand, and observed that the greatest measles importation risk is during December in which a high peak of travel occurs. Likewise, measles is probably imported from regions with both high travel rates (e.g., Australia, United Kingdom) and higher measles incidence (e.g., China, Indonesia).[[18]] During the COVID-19 pandemic, the risk of importing measles had been minimised due to the New Zealand border restrictions. With the opening of the borders in July 2022, together with the recent increase of measles cases in Africa and the East Mediterranean, there is an increased risk of measles importation through international travellers. Besides the risk of importing measles to New Zealand, a measles outbreak could also influence the risk of exporting measles to Pacific islands where health systems are more fragile.
Since the start of the COVID-19 pandemic, many countries have had disruptions of their routine immunisation services. Worldwide, coverage of the first dose of the measles vaccine has fallen about 7% from 2020 compared to 2019.[[19]] In New Zealand, MMR1 coverage was already declining before 2020, along with a declining trend in coverage for all childhood immunisations that has been observed since 2015.[[20]] Our study showed that a decreasing trend for MMR1 has been observed in all DHBs, emphasising that a national programme is needed to improve immunisation coverage. In the 2019 measles outbreak, the metropolitan area of Auckland was most affected with over half of the measles cases occurring in Counties Manukau. In children born between 2017 and 2018, the combined MMR1 coverage for Counties Manukau was 93.2% This emphasises that measles immunisation coverage needs to be higher to reduce the chances of transmission. It should be noted, however, that the immunity gap in adolescents could have played a role in this outbreak. Further, the previous outbreak could have increased the immunisation coverage in this area.
Immunisation coverage for measles varied by ethnicity with highest coverage rates in Asian children and lowest coverage in Māori. Previous research has shown that the higher immunisation rates in Asian children are mainly due to the positive attitude of parents towards timely vaccination of their children.[[21]] Immunisation coverage for MMR1 decreased by approximately 15% in Māori children comparing those born in 2017 to those born in 2020. This decrease is concerning, and public health resources should focus on improving immunisation coverage in this group in order to achieve equitable health outcomes. For instance, the emergency meningococcal C vaccination programme in 2011 reached equitable and high vaccination coverage.[[22]] In this programme, vaccination was promoted via various services. Vaccination programmes should include general practice services, community outreach clinics and involvement of Māori health providers.
Ideally, measles immunisation coverage should be >95% to reduce transmission. While, ideally, coverage should be boosted for both MMR1 and MMR2 the focus should initially be on MMR1 to have the greatest impact on preventing community spread of measles. In addition, immunisation programmes should consider focussing on improving coverage for other vaccines as well. Furthermore, healthcare accessibility should be ensured, including cultural safety in health services. Besides improvement of vaccine delivery including consistent involvement of Māori and Pasifika leadership and the use of mobile vaccination clinics, parental attitudes regarding vaccine safety should be addressed using effective communication. This is especially important as about 30% of the New Zealand population has concerns regarding vaccine safety.[[23,24]]
Strengths of this study include the detailed description of MMR1 and MMR2 coverage for young New Zealand children using high-quality data from the NIR.[[25]] In addition, we provided detailed geographical analyses of areas with high population density. This study has some limitations. Firstly, we did not study children born in 2021 as not all children in this birth cohort were eligible yet for their first MMR dose at 12 months. Data showing the overall immunisation coverage confirms the ongoing decreasing trend in the 2021 birth cohort.[[7]] Secondly, our data should be interpreted in light of the MMR programme change in 2020, with the second MMR dose thereafter being given at 15 months instead of 4 years of age. Therefore, children born in 2018 and in 2019 may not have been offered MMR2 before 4 years of age. Thirdly, we acknowledge that occurrence of a potential measles outbreak is also influenced by other factors such as crowding and immunisation coverage rates at children’s day cares.
Nevertheless, we focussed our analysis on young children as this group is most vulnerable to measles-related complications or even death.
Conclusions
Immunisation coverage rates for measles are currently insufficient to prevent a potential measles outbreak in children <5 years in New Zealand. Concerningly, the coverage for MMR1 is declining in all regions and especially in tamariki Māori. As young children are at high risk for measles-related complications, we urge the implementation of catch-up immunisation programmes to improve immunisation coverage.
View Appendices.
Summary
Abstract
Aim
To evaluate gaps in measles immunisation coverage for children<5 years in Aotearoa New Zealand.
Method
In this cross-sectional study, we extracted coverage rates for the first measles, mumps and rubella (MMR1) vaccine and second MMR vaccine (MMR2) from the National Immunisation Register for birth cohorts 2017 to 2020. We described measles coverage rates per birth cohort, and stratified per district health board (DHB), ethnicity and deprivation quintile.
Results
Coverage for MMR1 declined from 95.1% for those born in 2017 to 88.9% for those born in 2020. The coverage for MMR2 was below 90% for all the birth cohorts, with the lowest MMR2 coverage in the birth cohort of 2018 (61.6%). MMR1 coverage was lowest for children of Māori ethnicity and coverage declined over time: 92.8% for those born in 2017 to 78.4% for those born in 2020. Six DHBs had average MMR1 coverage <90% including Bay of Plenty, Lakes, Northland, Tairāwhiti, West Coast and Whanganui.
Conclusion
Immunisation coverage rates for measles are insufficient to prevent a potential measles outbreak in children <5 years. Concerningly, the coverage for MMR1 is declining, especially in Māori children. Catch-up immunisation programmes are urgently needed to improve immunisation coverage.
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
1) World Health Organization. Progress towards regional measles elimination, worldwide, 2000–2014. Wkly Epidemiol Rec. 2015;90:623-31.
2) World Health Organization [Internet]. Measles. Cited 13 June 2022. Available from: https://www.who.int/health-topics/measles#tab=tab_1.
3) Turner N. The challenge of improving immunization coverage: the New Zealand example. Expert Rev Vaccines. 2012;11(1):9-11.
4) Nowlan M, Willing E, Turner N. Influences and policies that affect immunisation coverage-a summary review of literature. N Z Med J. 2019; 132:79-88.
5) Turner N. A measles epidemic in New Zealand: Why did this occur and how can we prevent it occurring again? N Z Med J. 2019;132(1501):79-88.
6) Reynolds G, Dias C, Thornley S, et al. Analysis of the Auckland 2014 measles outbreak indicates that adolescents and young adults could benefit from catch-up vaccination. N Z Med J. 2015;128(1422):53-62.
7) Ministry of Health – Manatū Hauora [Internet]. National and DHB immunisation data. [Updated 2022 Apr 29; cited 2022 Jun 13.] Available from: https://www.health.govt.nz/our-work/preventative-health-wellness/immunisation/immunisation-coverage/national-and-dhb-immunisation-data.
8) Lassi ZS, Naseem R, Salam RA, Siddiqui F, Das JK. The Impact of the COVID-19 Pandemic on Immunization Campaigns and Programs: A Systematic Review. Int J Environ Res Public Health. 2021;18(3):988.
9) Hoang U, de Lusignan S, Joy M, et al. National rates and disparities in childhood vaccination and vaccine-preventable disease during the COVID-19 pandemic: English sentinel network retrospective database study. Arch Dis Child. 2022;107(8):733-739.
10) DeSilva MB, Haapala J, Vazquez-Benitez G, et al. Association of the COVID-19 Pandemic With Routine Childhood Vaccination Rates and Proportion Up to Date With Vaccinations Across 8 US Health Systems in the Vaccine Safety Datalink. JAMA Pediatr. 2022;176(1):68-77.
11) World Health Organization [Internet]. Immunization coverage. [Updated 2021 Jul 15; cited 2022 Jun 13.] Available from: https://www.who.int/news-room/fact-sheets/detail/immunization-coverage.
12) Institute of Environmental Science and Research (ESR) [Internet]. Measles report. [Cited 2022 Jun 13.] Available from: https://surv.esr.cri.nz/surveillance/WeeklyMeaslesRpt.php.
13) Craig AT, Heywood AE, Worth H. Measles epidemic in Samoa and other Pacific islands. Lancet Infect Dis. 2020;20(3):273-5.
14) World Health Organization [Internet]. UNICEF and WHO warn of perfect storm of conditions for measles outbreaks, affecting children. [Cited 2022 Jun 13.] Available from: https://www.who.int/news/item/27-04-2022-unicef-and-who-warn-of--perfect-storm--of-conditions-for-measles-outbreaks--affecting-children.
15) Atkinson J, Salmond C, Crampton P. NZDep2018 Index of Deprivation, Final Research Report. Department of Public Health, University of Otago, Wellington. December 2020.
16) Ministry of Health – Manatū Hauora [Internet]. Measles and Rubella Elimination in New Zealand, 2021 - Report to the 8th Meeting of the Western Pacific Regional Verification Commission for Measles and Rubella Elimination, 2021. Wellington, New Zealand; 2021.
17) World Health Organization. Global Health Observatory - Measles-containing-vaccine first-dose (MCV1) immunization coverage among 1-year-olds. [Updated 2022; cited 2022 Aug 29.] Available from: https://www.who.int/data/gho/data/indicators/indicator-details/GHO/measles-containing-vaccine-first-dose-(mcv1)-immunization-coverage-among-1-year-olds-(-).
18) Hayman DTS, Marshall JC, French NP, Carpenter TE, Roberts MG, Kiedrzynski T. Global importation and population risk factors for measles in New Zealand: a case study for highly immunized populations. Epidemiol Infect. 2017;145:1875-85.
19) Causey K, Fullman N, Sorensen RJD, et al. Estimating global and regional disruptions to routine childhood vaccine coverage during the COVID-19 pandemic in 2020: a modelling study. Lancet. 2021;398(10299):522-34.
20) Allen + Clarke [Internet]. Improving New Zealand’s childhood immunisation rates. Wellington; 2019. Available from: https://www.health.govt.nz/publication/improving-new-zealands-childhood-immunisation-rates.
21) Pal M, Goodyear-Smith F, Exeter D. Factors contributing to high immunisation coverage among New Zealand Asians. J Prim Health Care. 2014;6(4):304-11.
22) Mills C, Penney L. The Northland emergency meningococcal C vaccination programme. N Z Med J. 2013;126(1373):30-9.
23) Petousis-Harris H, Goodyear-Smith F, Turner N, Soe B. Family physician perspectives on barriers to childhood immunisation. Vaccine. 2004;22(17-18):2340-4.
24) Lee CHJ, Sibley CG. Attitudes toward vaccinations are becoming more polarized in New Zealand: Findings from a longitudinal survey. EClinicalMedicine. 2020;23.
25) Howe AS, Chisholm H, Paynter J, Willing E, Turner N. Does the National Immunisation Register stack up? Quantifying accuracy when compared to parent-held health record books. N Z Med J. 2021;134 (1541):22-32.
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Gaps in measles immunisation coverage for pre-school children in Aotearoa New Zealand: a cross-sectional study
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Measles is a highly contagious disease resulting from measles virus infection. Since the implementation of measles vaccines in the 1960s, incidence of measles and associated mortality have been largely reduced. Nevertheless, the global number of deaths that were attributed to measles was estimated to be over 140,000 in 2018, mainly occurring in low-income countries in Africa and Asia.[[1,2]] In particular, unvaccinated children under 5 years of age are at high risk for measles-related complications leading to hospital admission or even death.
Aotearoa New Zealand has notable immunity gaps in the population and the measles immunisation coverage target of ≥95% to prevent measles transmission has not yet been reached. Over the last few decades, following improvements in the national immunisation programme, immunisation coverage has increased (fully immunised at 2 years: 56% in 1992 to 91% in 2019).[[3,4]] For the birth cohorts of 1980–1999, the historically mediocre coverage rates have created an immunity gap due to insufficient measles immunity. Although catch-up immunisations have been offered, the immunisation coverage numbers for the birth cohorts of 1980–1999 are unclear.[[5,6]] Furthermore, in 2020 and 2021 New Zealand immunisation coverage rates have decreased relative to previous years (fully immunised at 2 years: 76% in 2020 and 85% in 2021), likely partly due to disrupted routine immunisation programmes early in the COVID-19 pandemic—a development that was also observed in other countries.[[7–11]] In addition, important differences in immunisation coverage exist between ethnicity groups, with lower coverage in Māori and Pacific peoples.
In 2017, New Zealand received a measles-free status following the absence of local transmission in the previous 3 years. Recent outbreaks in New Zealand have been linked to imported cases, and since a large outbreak in 2019 there have been no measles notifications.[[12]] Importantly, New Zealand is connected with the Pacific Islands and frequent travel across the Pacific occurs. Following the New Zealand measles outbreak in 2019, measles then spread to Samoa and caused a great impact with 83 deaths in a population of 200,874, of which 87% occurred in children <5 years.[[13]]
Since April 2022, measles outbreaks have been globally reported and have mainly occurred in Africa and the East Mediterranean region.[[14]] In July 2022, the New Zealand borders fully opened and, together with increasing measles cases worldwide, the likelihood of imported measles cases has increased. Identification of immunity gaps is important to specifically target public health resources. Therefore, in this study we aimed to describe gaps in immunisation coverage by ethnicity, socio-economic deprivation and region for measles in New Zealand children under 5 years of age.
Methods
Study design and the New Zealand measles immunisation programme
This was a cross-sectional study using publicly available data from the National Immunisation Register (NIR).[[7]] This study is exempt of ethics review as the study involved analysis of publicly available data that do not contain any sensitive health information. The data is held and curated by the New Zealand Ministry of Health.
The NIR records immunisation details for children born since 2005. Since 1 October 2020, the New Zealand immunisation schedule recommends that children to receive the first measles, mumps and rubella (MMR1) vaccine at 12 months (circa 95% seroconversion), and the second MMR (MMR2) vaccine at 15 months (circa 99% seroconversion). Prior to 1 October 2020, MMR dose one was administered at 15 months of age and MMR dose two was administered at 4 years of age. Following the measles outbreak in 2019, a measles immunisation campaign was implemented to improve immunisation rates. Activities for this campaign included maximising the uptake of MMR at 15 months and at 4 years with an active recall for children <5 years who had missed either of these two doses, and an MMR 0 dose for babies from 6–11 months old in the Auckland region.
Data collection
We extracted measles coverage rates for the MMR1 vaccine and the MMR2 vaccine for birth cohorts 2017 through 2020 on 22 June 2022. In these cohorts, all included children were offered MMR1. The MMR2 coverage rates, however, were influenced by the programme change in October 2020. Therefore, children who received MMR1 on time at 15 months may not have been offered a second dose before 4 years of age. Stratified data were extracted by prioritised ethnic group, by district health board (DHB) and by socio-economic deprivation quintile (1 to 5) defined by the New Zealand Deprivation Index 2018 (NZDep2018).[[15]] Deprivation quintile 1 represents areas with the least deprived scores, whereas deprivation quintile 5 represent areas with the most deprived scores. Though DHBs no longer exist as of mid-2022, for ease of interpretation and consistency with historical data, we retain the DHBs. We assessed population density using data from Statistics New Zealand. In addition, we collected data from previous measles outbreaks from the New Zealand Ministry of Health.
Data analysis
Firstly, we described MMR1 and MMR2 coverage rate, and whether the immunisation coverage rate was ≥90%. Although we planned a description of the MMR coverage target of ≥95%, we chose the 90% cut-off as none of the birth cohorts reached the 95% cut-off for MMR2. We combined data for the 2017–2020 birth cohorts, and also presented data for each birth cohort separately. Secondly, we stratified for ethnicity groups and per deprivation quintile. Thirdly, we illustrated MMR1 and MMR2 coverage per DHB using geographical heatmaps. Since DHBs comprise large areas and population density is a risk factor for a future measles outbreak, we performed a sub-group analysis of the 10 Territorial Authorities with the highest population density (Appendix 1). Next, since the Auckland region has the largest population, we performed a more detailed geographic analysis using coverage rates per the 2013 Area Unit (AU). In an urban setting such as Auckland, an AU is generally a collection of city blocks. Lastly, we described the DHBs with highest case and hospitalisation counts in the 2019 measles outbreak.[[16]] Children with missing data on deprivation quintile (<1%) or whose DHBs were classified “undefined or overseas” (<1%) were excluded from stratified analysis. All analyses were performed in R version 4.2.
Results
Overall MMR coverage
Overall, the coverage for MMR1 was 92.5% and the coverage for MMR2 was 74.6% for children born between 2017 and 2020. The coverage for MMR1 declined from 95.1% for those born in 2017 to 88.9% for those born in 2020 (Figure 1a). The coverage for MMR2 was below 90% for the studied birth cohorts: the lowest MMR2 coverage was observed for the birth cohort of 2018 (61.6%). MMR2 coverage increased for those born in 2019 (72.8%) and in 2020 (80.3%).
View Figures 1–3 and Table 1.
MMR coverage per ethnicity
Coverage for MMR1 was above 90% in all birth cohorts for children of Asian ethnicity (range 97.6% to 98.4%), NZ European ethnicity (range 91.7% to 94.8%) and children of other ethnicity (range 90.1% to 93.7%) (Figure 1a). MMR1 coverage was lowest for children of Māori ethnicity and coverage declined over time: from 92.8% for the 2017 birth cohort to 78.4% for the 2020 birth cohort. For Pacific children MMR1 coverage was above 90% for those born in 2017 to 2019 (range 92.3% to 97.0%) but was 88.3% for those born in 2020.
MMR2 coverage was <90% for all birth cohorts in each ethnic group, with the exception of children of Asian ethnicity in the birth cohorts of 2017 and 2020 (Figure 1b). For all the ethnicity groups, MMR2 coverage was lowest for the 2018 cohort (NZ European 66.1%; Māori 48.4%; Pacific 55.5%; Asian 72.7%; Other 63.6%). MMR2 coverage increased for all the ethnicities in the birth cohorts of 2019 and 2020, although coverage has not yet reached the 2017 level for children of Māori, Pacific and NZ European ethnicities.
MMR coverage per socio-economic deprivation quintile
MMR1 and MMR2 coverage was lower in the more socio-economically deprived areas compared to less deprived areas (Appendix 3). The difference of MMR1 coverage between the least deprived areas and the most deprived areas increased from 1.7% in birth cohort 2017 to 9.2% in birth cohort 2020. The difference of MMR2 coverage between the least deprived areas and the most deprived areas ranged from 12.5% (birth cohort 2017) to 17.5% (birth cohort 2018), and was around 15% for birth cohorts 2019 and 2020.
MMR coverage per DHB level
Across the birth cohorts, MMR1 coverage decreased in all DHBs (Figure 2). Six DHBs had an average MMR1 coverage <90% (Bay of Plenty, Lakes, Northland, Tairāwhiti, West Coast and Whanganui). None of the DHBs had MMR2 coverage >90% (Figure 3). For the birth cohorts 2017–2020 combined, the lowest MMR2 coverage was observed in Northland (59.1%), Waikato (61.2%) and Lakes (62.1%) (Appendix 4).
MMR coverage for top 10 population density areas
The 10 areas with the highest population density are presented in Table 1. The average MMR1 coverage was below 90% for Kawerau and Tauranga. Apart from Wellington, the other areas all had MMR2 coverage <90%. Average MMR2 coverage was lowest for Hamilton (62.8%), Napier (68.9%) and Auckland (73.8%).
For all birth cohorts, coverage for Auckland was above 90% for MMR1 (range 92.3% to 96.6%) whereas coverage for MMR2 was below <90% (range 67.4% to 83.7%). MMR1 and MMR2 coverage varied across AUs for Auckland (Figure 2 and Figure 3). For the Auckland area, the number of AUs with MMR1 coverage <90% increased from 2/106 (1.9%) in birth cohort 2017 to 26/106 (24.5%) in birth cohort 2020. For almost all AUs, MMR2 coverage was <90% for those born in 2018 (101/106, 95%) and in 2019 (98/106, 92.5%).
2019 measles outbreak
In the 2019 measles outbreak the Auckland metropolitan area was most affected. The DHBs with the highest measles incidence in the 2019 outbreak included Counties Manukau (measles incidence 202 cases per 100,000; hospitalisation rate 77 cases per 100,000), Northland, Auckland and Waitematā (Appendix 5). In these DHBs, MMR1 coverage decreased across the different birth cohorts. For the 2017 and the 2018 birth cohorts combined, the MMR1 coverage was 93.2% in Counties Manukau, 84.4% in Northland, 95.1% in Auckland and 93.8% in Waitematā. For those born in 2020, MMR1 coverage was 89.2% in Counties Manukau, 77.0% in Northland, 92.2% in Auckland and 90.3% in Waitematā.
Discussion
In this cross-sectional study, we assessed measles vaccine coverage rates in young children in New Zealand. Concerningly, coverage for MMR1 has been declining, especially in Māori children. In addition, MMR1 coverage declined in all DHBs, with six DHBs having average MMR1 coverage <90% for the birth cohorts of 2017 to 2020. Immunisation coverage for measles is therefore insufficient to prevent community transmission in young children.
Globally, the World Health Organization reported that coverage of at least one dose of measles vaccine was 81% in children 2 years of age in 2020. For children in New Zealand born between 2017 and 2020, the MMR1 coverage is 92.5%, which is higher compared to the global average, and is similar to the coverage in other high-income countries (MMR1 93%).[[17]] In order to prevent measles transmission in New Zealand, the current coverage should be increased to reach the 95% target.
The heterogeneous immunity in the New Zealand population remains a risk factor for any future measles outbreak. Contributing factors to the 2019 measles outbreak included the recent decline in infant immunisation coverage in addition to the immunity gap in young adults, especially those of Māori or Pacific ethnicity.[[5]] Our study focussed on the description of immunisation coverage in young children as this group is at highest risk for measles-related complications. We acknowledge the lower immunisation coverage in young adults, who may have a key role in the importation and transmission of measles in New Zealand communities. However, these cohorts received MMR vaccines prior to the commencement of the NIR, which makes accurate estimates of coverage challenging. To address the immunity gap in young people both up-to-date immunisation records and the immunisation coverage should be improved.[[5,6]]
Hayman et al. analysed risk factors for measles up to 2014 in New Zealand, and observed that the greatest measles importation risk is during December in which a high peak of travel occurs. Likewise, measles is probably imported from regions with both high travel rates (e.g., Australia, United Kingdom) and higher measles incidence (e.g., China, Indonesia).[[18]] During the COVID-19 pandemic, the risk of importing measles had been minimised due to the New Zealand border restrictions. With the opening of the borders in July 2022, together with the recent increase of measles cases in Africa and the East Mediterranean, there is an increased risk of measles importation through international travellers. Besides the risk of importing measles to New Zealand, a measles outbreak could also influence the risk of exporting measles to Pacific islands where health systems are more fragile.
Since the start of the COVID-19 pandemic, many countries have had disruptions of their routine immunisation services. Worldwide, coverage of the first dose of the measles vaccine has fallen about 7% from 2020 compared to 2019.[[19]] In New Zealand, MMR1 coverage was already declining before 2020, along with a declining trend in coverage for all childhood immunisations that has been observed since 2015.[[20]] Our study showed that a decreasing trend for MMR1 has been observed in all DHBs, emphasising that a national programme is needed to improve immunisation coverage. In the 2019 measles outbreak, the metropolitan area of Auckland was most affected with over half of the measles cases occurring in Counties Manukau. In children born between 2017 and 2018, the combined MMR1 coverage for Counties Manukau was 93.2% This emphasises that measles immunisation coverage needs to be higher to reduce the chances of transmission. It should be noted, however, that the immunity gap in adolescents could have played a role in this outbreak. Further, the previous outbreak could have increased the immunisation coverage in this area.
Immunisation coverage for measles varied by ethnicity with highest coverage rates in Asian children and lowest coverage in Māori. Previous research has shown that the higher immunisation rates in Asian children are mainly due to the positive attitude of parents towards timely vaccination of their children.[[21]] Immunisation coverage for MMR1 decreased by approximately 15% in Māori children comparing those born in 2017 to those born in 2020. This decrease is concerning, and public health resources should focus on improving immunisation coverage in this group in order to achieve equitable health outcomes. For instance, the emergency meningococcal C vaccination programme in 2011 reached equitable and high vaccination coverage.[[22]] In this programme, vaccination was promoted via various services. Vaccination programmes should include general practice services, community outreach clinics and involvement of Māori health providers.
Ideally, measles immunisation coverage should be >95% to reduce transmission. While, ideally, coverage should be boosted for both MMR1 and MMR2 the focus should initially be on MMR1 to have the greatest impact on preventing community spread of measles. In addition, immunisation programmes should consider focussing on improving coverage for other vaccines as well. Furthermore, healthcare accessibility should be ensured, including cultural safety in health services. Besides improvement of vaccine delivery including consistent involvement of Māori and Pasifika leadership and the use of mobile vaccination clinics, parental attitudes regarding vaccine safety should be addressed using effective communication. This is especially important as about 30% of the New Zealand population has concerns regarding vaccine safety.[[23,24]]
Strengths of this study include the detailed description of MMR1 and MMR2 coverage for young New Zealand children using high-quality data from the NIR.[[25]] In addition, we provided detailed geographical analyses of areas with high population density. This study has some limitations. Firstly, we did not study children born in 2021 as not all children in this birth cohort were eligible yet for their first MMR dose at 12 months. Data showing the overall immunisation coverage confirms the ongoing decreasing trend in the 2021 birth cohort.[[7]] Secondly, our data should be interpreted in light of the MMR programme change in 2020, with the second MMR dose thereafter being given at 15 months instead of 4 years of age. Therefore, children born in 2018 and in 2019 may not have been offered MMR2 before 4 years of age. Thirdly, we acknowledge that occurrence of a potential measles outbreak is also influenced by other factors such as crowding and immunisation coverage rates at children’s day cares.
Nevertheless, we focussed our analysis on young children as this group is most vulnerable to measles-related complications or even death.
Conclusions
Immunisation coverage rates for measles are currently insufficient to prevent a potential measles outbreak in children <5 years in New Zealand. Concerningly, the coverage for MMR1 is declining in all regions and especially in tamariki Māori. As young children are at high risk for measles-related complications, we urge the implementation of catch-up immunisation programmes to improve immunisation coverage.
View Appendices.
Summary
Abstract
Aim
To evaluate gaps in measles immunisation coverage for children<5 years in Aotearoa New Zealand.
Method
In this cross-sectional study, we extracted coverage rates for the first measles, mumps and rubella (MMR1) vaccine and second MMR vaccine (MMR2) from the National Immunisation Register for birth cohorts 2017 to 2020. We described measles coverage rates per birth cohort, and stratified per district health board (DHB), ethnicity and deprivation quintile.
Results
Coverage for MMR1 declined from 95.1% for those born in 2017 to 88.9% for those born in 2020. The coverage for MMR2 was below 90% for all the birth cohorts, with the lowest MMR2 coverage in the birth cohort of 2018 (61.6%). MMR1 coverage was lowest for children of Māori ethnicity and coverage declined over time: 92.8% for those born in 2017 to 78.4% for those born in 2020. Six DHBs had average MMR1 coverage <90% including Bay of Plenty, Lakes, Northland, Tairāwhiti, West Coast and Whanganui.
Conclusion
Immunisation coverage rates for measles are insufficient to prevent a potential measles outbreak in children <5 years. Concerningly, the coverage for MMR1 is declining, especially in Māori children. Catch-up immunisation programmes are urgently needed to improve immunisation coverage.
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
1) World Health Organization. Progress towards regional measles elimination, worldwide, 2000–2014. Wkly Epidemiol Rec. 2015;90:623-31.
2) World Health Organization [Internet]. Measles. Cited 13 June 2022. Available from: https://www.who.int/health-topics/measles#tab=tab_1.
3) Turner N. The challenge of improving immunization coverage: the New Zealand example. Expert Rev Vaccines. 2012;11(1):9-11.
4) Nowlan M, Willing E, Turner N. Influences and policies that affect immunisation coverage-a summary review of literature. N Z Med J. 2019; 132:79-88.
5) Turner N. A measles epidemic in New Zealand: Why did this occur and how can we prevent it occurring again? N Z Med J. 2019;132(1501):79-88.
6) Reynolds G, Dias C, Thornley S, et al. Analysis of the Auckland 2014 measles outbreak indicates that adolescents and young adults could benefit from catch-up vaccination. N Z Med J. 2015;128(1422):53-62.
7) Ministry of Health – Manatū Hauora [Internet]. National and DHB immunisation data. [Updated 2022 Apr 29; cited 2022 Jun 13.] Available from: https://www.health.govt.nz/our-work/preventative-health-wellness/immunisation/immunisation-coverage/national-and-dhb-immunisation-data.
8) Lassi ZS, Naseem R, Salam RA, Siddiqui F, Das JK. The Impact of the COVID-19 Pandemic on Immunization Campaigns and Programs: A Systematic Review. Int J Environ Res Public Health. 2021;18(3):988.
9) Hoang U, de Lusignan S, Joy M, et al. National rates and disparities in childhood vaccination and vaccine-preventable disease during the COVID-19 pandemic: English sentinel network retrospective database study. Arch Dis Child. 2022;107(8):733-739.
10) DeSilva MB, Haapala J, Vazquez-Benitez G, et al. Association of the COVID-19 Pandemic With Routine Childhood Vaccination Rates and Proportion Up to Date With Vaccinations Across 8 US Health Systems in the Vaccine Safety Datalink. JAMA Pediatr. 2022;176(1):68-77.
11) World Health Organization [Internet]. Immunization coverage. [Updated 2021 Jul 15; cited 2022 Jun 13.] Available from: https://www.who.int/news-room/fact-sheets/detail/immunization-coverage.
12) Institute of Environmental Science and Research (ESR) [Internet]. Measles report. [Cited 2022 Jun 13.] Available from: https://surv.esr.cri.nz/surveillance/WeeklyMeaslesRpt.php.
13) Craig AT, Heywood AE, Worth H. Measles epidemic in Samoa and other Pacific islands. Lancet Infect Dis. 2020;20(3):273-5.
14) World Health Organization [Internet]. UNICEF and WHO warn of perfect storm of conditions for measles outbreaks, affecting children. [Cited 2022 Jun 13.] Available from: https://www.who.int/news/item/27-04-2022-unicef-and-who-warn-of--perfect-storm--of-conditions-for-measles-outbreaks--affecting-children.
15) Atkinson J, Salmond C, Crampton P. NZDep2018 Index of Deprivation, Final Research Report. Department of Public Health, University of Otago, Wellington. December 2020.
16) Ministry of Health – Manatū Hauora [Internet]. Measles and Rubella Elimination in New Zealand, 2021 - Report to the 8th Meeting of the Western Pacific Regional Verification Commission for Measles and Rubella Elimination, 2021. Wellington, New Zealand; 2021.
17) World Health Organization. Global Health Observatory - Measles-containing-vaccine first-dose (MCV1) immunization coverage among 1-year-olds. [Updated 2022; cited 2022 Aug 29.] Available from: https://www.who.int/data/gho/data/indicators/indicator-details/GHO/measles-containing-vaccine-first-dose-(mcv1)-immunization-coverage-among-1-year-olds-(-).
18) Hayman DTS, Marshall JC, French NP, Carpenter TE, Roberts MG, Kiedrzynski T. Global importation and population risk factors for measles in New Zealand: a case study for highly immunized populations. Epidemiol Infect. 2017;145:1875-85.
19) Causey K, Fullman N, Sorensen RJD, et al. Estimating global and regional disruptions to routine childhood vaccine coverage during the COVID-19 pandemic in 2020: a modelling study. Lancet. 2021;398(10299):522-34.
20) Allen + Clarke [Internet]. Improving New Zealand’s childhood immunisation rates. Wellington; 2019. Available from: https://www.health.govt.nz/publication/improving-new-zealands-childhood-immunisation-rates.
21) Pal M, Goodyear-Smith F, Exeter D. Factors contributing to high immunisation coverage among New Zealand Asians. J Prim Health Care. 2014;6(4):304-11.
22) Mills C, Penney L. The Northland emergency meningococcal C vaccination programme. N Z Med J. 2013;126(1373):30-9.
23) Petousis-Harris H, Goodyear-Smith F, Turner N, Soe B. Family physician perspectives on barriers to childhood immunisation. Vaccine. 2004;22(17-18):2340-4.
24) Lee CHJ, Sibley CG. Attitudes toward vaccinations are becoming more polarized in New Zealand: Findings from a longitudinal survey. EClinicalMedicine. 2020;23.
25) Howe AS, Chisholm H, Paynter J, Willing E, Turner N. Does the National Immunisation Register stack up? Quantifying accuracy when compared to parent-held health record books. N Z Med J. 2021;134 (1541):22-32.
Contact diana@nzma.org.nz
for the PDF of this article
Gaps in measles immunisation coverage for pre-school children in Aotearoa New Zealand: a cross-sectional study
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Measles is a highly contagious disease resulting from measles virus infection. Since the implementation of measles vaccines in the 1960s, incidence of measles and associated mortality have been largely reduced. Nevertheless, the global number of deaths that were attributed to measles was estimated to be over 140,000 in 2018, mainly occurring in low-income countries in Africa and Asia.[[1,2]] In particular, unvaccinated children under 5 years of age are at high risk for measles-related complications leading to hospital admission or even death.
Aotearoa New Zealand has notable immunity gaps in the population and the measles immunisation coverage target of ≥95% to prevent measles transmission has not yet been reached. Over the last few decades, following improvements in the national immunisation programme, immunisation coverage has increased (fully immunised at 2 years: 56% in 1992 to 91% in 2019).[[3,4]] For the birth cohorts of 1980–1999, the historically mediocre coverage rates have created an immunity gap due to insufficient measles immunity. Although catch-up immunisations have been offered, the immunisation coverage numbers for the birth cohorts of 1980–1999 are unclear.[[5,6]] Furthermore, in 2020 and 2021 New Zealand immunisation coverage rates have decreased relative to previous years (fully immunised at 2 years: 76% in 2020 and 85% in 2021), likely partly due to disrupted routine immunisation programmes early in the COVID-19 pandemic—a development that was also observed in other countries.[[7–11]] In addition, important differences in immunisation coverage exist between ethnicity groups, with lower coverage in Māori and Pacific peoples.
In 2017, New Zealand received a measles-free status following the absence of local transmission in the previous 3 years. Recent outbreaks in New Zealand have been linked to imported cases, and since a large outbreak in 2019 there have been no measles notifications.[[12]] Importantly, New Zealand is connected with the Pacific Islands and frequent travel across the Pacific occurs. Following the New Zealand measles outbreak in 2019, measles then spread to Samoa and caused a great impact with 83 deaths in a population of 200,874, of which 87% occurred in children <5 years.[[13]]
Since April 2022, measles outbreaks have been globally reported and have mainly occurred in Africa and the East Mediterranean region.[[14]] In July 2022, the New Zealand borders fully opened and, together with increasing measles cases worldwide, the likelihood of imported measles cases has increased. Identification of immunity gaps is important to specifically target public health resources. Therefore, in this study we aimed to describe gaps in immunisation coverage by ethnicity, socio-economic deprivation and region for measles in New Zealand children under 5 years of age.
Methods
Study design and the New Zealand measles immunisation programme
This was a cross-sectional study using publicly available data from the National Immunisation Register (NIR).[[7]] This study is exempt of ethics review as the study involved analysis of publicly available data that do not contain any sensitive health information. The data is held and curated by the New Zealand Ministry of Health.
The NIR records immunisation details for children born since 2005. Since 1 October 2020, the New Zealand immunisation schedule recommends that children to receive the first measles, mumps and rubella (MMR1) vaccine at 12 months (circa 95% seroconversion), and the second MMR (MMR2) vaccine at 15 months (circa 99% seroconversion). Prior to 1 October 2020, MMR dose one was administered at 15 months of age and MMR dose two was administered at 4 years of age. Following the measles outbreak in 2019, a measles immunisation campaign was implemented to improve immunisation rates. Activities for this campaign included maximising the uptake of MMR at 15 months and at 4 years with an active recall for children <5 years who had missed either of these two doses, and an MMR 0 dose for babies from 6–11 months old in the Auckland region.
Data collection
We extracted measles coverage rates for the MMR1 vaccine and the MMR2 vaccine for birth cohorts 2017 through 2020 on 22 June 2022. In these cohorts, all included children were offered MMR1. The MMR2 coverage rates, however, were influenced by the programme change in October 2020. Therefore, children who received MMR1 on time at 15 months may not have been offered a second dose before 4 years of age. Stratified data were extracted by prioritised ethnic group, by district health board (DHB) and by socio-economic deprivation quintile (1 to 5) defined by the New Zealand Deprivation Index 2018 (NZDep2018).[[15]] Deprivation quintile 1 represents areas with the least deprived scores, whereas deprivation quintile 5 represent areas with the most deprived scores. Though DHBs no longer exist as of mid-2022, for ease of interpretation and consistency with historical data, we retain the DHBs. We assessed population density using data from Statistics New Zealand. In addition, we collected data from previous measles outbreaks from the New Zealand Ministry of Health.
Data analysis
Firstly, we described MMR1 and MMR2 coverage rate, and whether the immunisation coverage rate was ≥90%. Although we planned a description of the MMR coverage target of ≥95%, we chose the 90% cut-off as none of the birth cohorts reached the 95% cut-off for MMR2. We combined data for the 2017–2020 birth cohorts, and also presented data for each birth cohort separately. Secondly, we stratified for ethnicity groups and per deprivation quintile. Thirdly, we illustrated MMR1 and MMR2 coverage per DHB using geographical heatmaps. Since DHBs comprise large areas and population density is a risk factor for a future measles outbreak, we performed a sub-group analysis of the 10 Territorial Authorities with the highest population density (Appendix 1). Next, since the Auckland region has the largest population, we performed a more detailed geographic analysis using coverage rates per the 2013 Area Unit (AU). In an urban setting such as Auckland, an AU is generally a collection of city blocks. Lastly, we described the DHBs with highest case and hospitalisation counts in the 2019 measles outbreak.[[16]] Children with missing data on deprivation quintile (<1%) or whose DHBs were classified “undefined or overseas” (<1%) were excluded from stratified analysis. All analyses were performed in R version 4.2.
Results
Overall MMR coverage
Overall, the coverage for MMR1 was 92.5% and the coverage for MMR2 was 74.6% for children born between 2017 and 2020. The coverage for MMR1 declined from 95.1% for those born in 2017 to 88.9% for those born in 2020 (Figure 1a). The coverage for MMR2 was below 90% for the studied birth cohorts: the lowest MMR2 coverage was observed for the birth cohort of 2018 (61.6%). MMR2 coverage increased for those born in 2019 (72.8%) and in 2020 (80.3%).
View Figures 1–3 and Table 1.
MMR coverage per ethnicity
Coverage for MMR1 was above 90% in all birth cohorts for children of Asian ethnicity (range 97.6% to 98.4%), NZ European ethnicity (range 91.7% to 94.8%) and children of other ethnicity (range 90.1% to 93.7%) (Figure 1a). MMR1 coverage was lowest for children of Māori ethnicity and coverage declined over time: from 92.8% for the 2017 birth cohort to 78.4% for the 2020 birth cohort. For Pacific children MMR1 coverage was above 90% for those born in 2017 to 2019 (range 92.3% to 97.0%) but was 88.3% for those born in 2020.
MMR2 coverage was <90% for all birth cohorts in each ethnic group, with the exception of children of Asian ethnicity in the birth cohorts of 2017 and 2020 (Figure 1b). For all the ethnicity groups, MMR2 coverage was lowest for the 2018 cohort (NZ European 66.1%; Māori 48.4%; Pacific 55.5%; Asian 72.7%; Other 63.6%). MMR2 coverage increased for all the ethnicities in the birth cohorts of 2019 and 2020, although coverage has not yet reached the 2017 level for children of Māori, Pacific and NZ European ethnicities.
MMR coverage per socio-economic deprivation quintile
MMR1 and MMR2 coverage was lower in the more socio-economically deprived areas compared to less deprived areas (Appendix 3). The difference of MMR1 coverage between the least deprived areas and the most deprived areas increased from 1.7% in birth cohort 2017 to 9.2% in birth cohort 2020. The difference of MMR2 coverage between the least deprived areas and the most deprived areas ranged from 12.5% (birth cohort 2017) to 17.5% (birth cohort 2018), and was around 15% for birth cohorts 2019 and 2020.
MMR coverage per DHB level
Across the birth cohorts, MMR1 coverage decreased in all DHBs (Figure 2). Six DHBs had an average MMR1 coverage <90% (Bay of Plenty, Lakes, Northland, Tairāwhiti, West Coast and Whanganui). None of the DHBs had MMR2 coverage >90% (Figure 3). For the birth cohorts 2017–2020 combined, the lowest MMR2 coverage was observed in Northland (59.1%), Waikato (61.2%) and Lakes (62.1%) (Appendix 4).
MMR coverage for top 10 population density areas
The 10 areas with the highest population density are presented in Table 1. The average MMR1 coverage was below 90% for Kawerau and Tauranga. Apart from Wellington, the other areas all had MMR2 coverage <90%. Average MMR2 coverage was lowest for Hamilton (62.8%), Napier (68.9%) and Auckland (73.8%).
For all birth cohorts, coverage for Auckland was above 90% for MMR1 (range 92.3% to 96.6%) whereas coverage for MMR2 was below <90% (range 67.4% to 83.7%). MMR1 and MMR2 coverage varied across AUs for Auckland (Figure 2 and Figure 3). For the Auckland area, the number of AUs with MMR1 coverage <90% increased from 2/106 (1.9%) in birth cohort 2017 to 26/106 (24.5%) in birth cohort 2020. For almost all AUs, MMR2 coverage was <90% for those born in 2018 (101/106, 95%) and in 2019 (98/106, 92.5%).
2019 measles outbreak
In the 2019 measles outbreak the Auckland metropolitan area was most affected. The DHBs with the highest measles incidence in the 2019 outbreak included Counties Manukau (measles incidence 202 cases per 100,000; hospitalisation rate 77 cases per 100,000), Northland, Auckland and Waitematā (Appendix 5). In these DHBs, MMR1 coverage decreased across the different birth cohorts. For the 2017 and the 2018 birth cohorts combined, the MMR1 coverage was 93.2% in Counties Manukau, 84.4% in Northland, 95.1% in Auckland and 93.8% in Waitematā. For those born in 2020, MMR1 coverage was 89.2% in Counties Manukau, 77.0% in Northland, 92.2% in Auckland and 90.3% in Waitematā.
Discussion
In this cross-sectional study, we assessed measles vaccine coverage rates in young children in New Zealand. Concerningly, coverage for MMR1 has been declining, especially in Māori children. In addition, MMR1 coverage declined in all DHBs, with six DHBs having average MMR1 coverage <90% for the birth cohorts of 2017 to 2020. Immunisation coverage for measles is therefore insufficient to prevent community transmission in young children.
Globally, the World Health Organization reported that coverage of at least one dose of measles vaccine was 81% in children 2 years of age in 2020. For children in New Zealand born between 2017 and 2020, the MMR1 coverage is 92.5%, which is higher compared to the global average, and is similar to the coverage in other high-income countries (MMR1 93%).[[17]] In order to prevent measles transmission in New Zealand, the current coverage should be increased to reach the 95% target.
The heterogeneous immunity in the New Zealand population remains a risk factor for any future measles outbreak. Contributing factors to the 2019 measles outbreak included the recent decline in infant immunisation coverage in addition to the immunity gap in young adults, especially those of Māori or Pacific ethnicity.[[5]] Our study focussed on the description of immunisation coverage in young children as this group is at highest risk for measles-related complications. We acknowledge the lower immunisation coverage in young adults, who may have a key role in the importation and transmission of measles in New Zealand communities. However, these cohorts received MMR vaccines prior to the commencement of the NIR, which makes accurate estimates of coverage challenging. To address the immunity gap in young people both up-to-date immunisation records and the immunisation coverage should be improved.[[5,6]]
Hayman et al. analysed risk factors for measles up to 2014 in New Zealand, and observed that the greatest measles importation risk is during December in which a high peak of travel occurs. Likewise, measles is probably imported from regions with both high travel rates (e.g., Australia, United Kingdom) and higher measles incidence (e.g., China, Indonesia).[[18]] During the COVID-19 pandemic, the risk of importing measles had been minimised due to the New Zealand border restrictions. With the opening of the borders in July 2022, together with the recent increase of measles cases in Africa and the East Mediterranean, there is an increased risk of measles importation through international travellers. Besides the risk of importing measles to New Zealand, a measles outbreak could also influence the risk of exporting measles to Pacific islands where health systems are more fragile.
Since the start of the COVID-19 pandemic, many countries have had disruptions of their routine immunisation services. Worldwide, coverage of the first dose of the measles vaccine has fallen about 7% from 2020 compared to 2019.[[19]] In New Zealand, MMR1 coverage was already declining before 2020, along with a declining trend in coverage for all childhood immunisations that has been observed since 2015.[[20]] Our study showed that a decreasing trend for MMR1 has been observed in all DHBs, emphasising that a national programme is needed to improve immunisation coverage. In the 2019 measles outbreak, the metropolitan area of Auckland was most affected with over half of the measles cases occurring in Counties Manukau. In children born between 2017 and 2018, the combined MMR1 coverage for Counties Manukau was 93.2% This emphasises that measles immunisation coverage needs to be higher to reduce the chances of transmission. It should be noted, however, that the immunity gap in adolescents could have played a role in this outbreak. Further, the previous outbreak could have increased the immunisation coverage in this area.
Immunisation coverage for measles varied by ethnicity with highest coverage rates in Asian children and lowest coverage in Māori. Previous research has shown that the higher immunisation rates in Asian children are mainly due to the positive attitude of parents towards timely vaccination of their children.[[21]] Immunisation coverage for MMR1 decreased by approximately 15% in Māori children comparing those born in 2017 to those born in 2020. This decrease is concerning, and public health resources should focus on improving immunisation coverage in this group in order to achieve equitable health outcomes. For instance, the emergency meningococcal C vaccination programme in 2011 reached equitable and high vaccination coverage.[[22]] In this programme, vaccination was promoted via various services. Vaccination programmes should include general practice services, community outreach clinics and involvement of Māori health providers.
Ideally, measles immunisation coverage should be >95% to reduce transmission. While, ideally, coverage should be boosted for both MMR1 and MMR2 the focus should initially be on MMR1 to have the greatest impact on preventing community spread of measles. In addition, immunisation programmes should consider focussing on improving coverage for other vaccines as well. Furthermore, healthcare accessibility should be ensured, including cultural safety in health services. Besides improvement of vaccine delivery including consistent involvement of Māori and Pasifika leadership and the use of mobile vaccination clinics, parental attitudes regarding vaccine safety should be addressed using effective communication. This is especially important as about 30% of the New Zealand population has concerns regarding vaccine safety.[[23,24]]
Strengths of this study include the detailed description of MMR1 and MMR2 coverage for young New Zealand children using high-quality data from the NIR.[[25]] In addition, we provided detailed geographical analyses of areas with high population density. This study has some limitations. Firstly, we did not study children born in 2021 as not all children in this birth cohort were eligible yet for their first MMR dose at 12 months. Data showing the overall immunisation coverage confirms the ongoing decreasing trend in the 2021 birth cohort.[[7]] Secondly, our data should be interpreted in light of the MMR programme change in 2020, with the second MMR dose thereafter being given at 15 months instead of 4 years of age. Therefore, children born in 2018 and in 2019 may not have been offered MMR2 before 4 years of age. Thirdly, we acknowledge that occurrence of a potential measles outbreak is also influenced by other factors such as crowding and immunisation coverage rates at children’s day cares.
Nevertheless, we focussed our analysis on young children as this group is most vulnerable to measles-related complications or even death.
Conclusions
Immunisation coverage rates for measles are currently insufficient to prevent a potential measles outbreak in children <5 years in New Zealand. Concerningly, the coverage for MMR1 is declining in all regions and especially in tamariki Māori. As young children are at high risk for measles-related complications, we urge the implementation of catch-up immunisation programmes to improve immunisation coverage.
View Appendices.
Summary
Abstract
Aim
To evaluate gaps in measles immunisation coverage for children<5 years in Aotearoa New Zealand.
Method
In this cross-sectional study, we extracted coverage rates for the first measles, mumps and rubella (MMR1) vaccine and second MMR vaccine (MMR2) from the National Immunisation Register for birth cohorts 2017 to 2020. We described measles coverage rates per birth cohort, and stratified per district health board (DHB), ethnicity and deprivation quintile.
Results
Coverage for MMR1 declined from 95.1% for those born in 2017 to 88.9% for those born in 2020. The coverage for MMR2 was below 90% for all the birth cohorts, with the lowest MMR2 coverage in the birth cohort of 2018 (61.6%). MMR1 coverage was lowest for children of Māori ethnicity and coverage declined over time: 92.8% for those born in 2017 to 78.4% for those born in 2020. Six DHBs had average MMR1 coverage <90% including Bay of Plenty, Lakes, Northland, Tairāwhiti, West Coast and Whanganui.
Conclusion
Immunisation coverage rates for measles are insufficient to prevent a potential measles outbreak in children <5 years. Concerningly, the coverage for MMR1 is declining, especially in Māori children. Catch-up immunisation programmes are urgently needed to improve immunisation coverage.
Author Information
Acknowledgements
Correspondence
Correspondence Email
Competing Interests
1) World Health Organization. Progress towards regional measles elimination, worldwide, 2000–2014. Wkly Epidemiol Rec. 2015;90:623-31.
2) World Health Organization [Internet]. Measles. Cited 13 June 2022. Available from: https://www.who.int/health-topics/measles#tab=tab_1.
3) Turner N. The challenge of improving immunization coverage: the New Zealand example. Expert Rev Vaccines. 2012;11(1):9-11.
4) Nowlan M, Willing E, Turner N. Influences and policies that affect immunisation coverage-a summary review of literature. N Z Med J. 2019; 132:79-88.
5) Turner N. A measles epidemic in New Zealand: Why did this occur and how can we prevent it occurring again? N Z Med J. 2019;132(1501):79-88.
6) Reynolds G, Dias C, Thornley S, et al. Analysis of the Auckland 2014 measles outbreak indicates that adolescents and young adults could benefit from catch-up vaccination. N Z Med J. 2015;128(1422):53-62.
7) Ministry of Health – Manatū Hauora [Internet]. National and DHB immunisation data. [Updated 2022 Apr 29; cited 2022 Jun 13.] Available from: https://www.health.govt.nz/our-work/preventative-health-wellness/immunisation/immunisation-coverage/national-and-dhb-immunisation-data.
8) Lassi ZS, Naseem R, Salam RA, Siddiqui F, Das JK. The Impact of the COVID-19 Pandemic on Immunization Campaigns and Programs: A Systematic Review. Int J Environ Res Public Health. 2021;18(3):988.
9) Hoang U, de Lusignan S, Joy M, et al. National rates and disparities in childhood vaccination and vaccine-preventable disease during the COVID-19 pandemic: English sentinel network retrospective database study. Arch Dis Child. 2022;107(8):733-739.
10) DeSilva MB, Haapala J, Vazquez-Benitez G, et al. Association of the COVID-19 Pandemic With Routine Childhood Vaccination Rates and Proportion Up to Date With Vaccinations Across 8 US Health Systems in the Vaccine Safety Datalink. JAMA Pediatr. 2022;176(1):68-77.
11) World Health Organization [Internet]. Immunization coverage. [Updated 2021 Jul 15; cited 2022 Jun 13.] Available from: https://www.who.int/news-room/fact-sheets/detail/immunization-coverage.
12) Institute of Environmental Science and Research (ESR) [Internet]. Measles report. [Cited 2022 Jun 13.] Available from: https://surv.esr.cri.nz/surveillance/WeeklyMeaslesRpt.php.
13) Craig AT, Heywood AE, Worth H. Measles epidemic in Samoa and other Pacific islands. Lancet Infect Dis. 2020;20(3):273-5.
14) World Health Organization [Internet]. UNICEF and WHO warn of perfect storm of conditions for measles outbreaks, affecting children. [Cited 2022 Jun 13.] Available from: https://www.who.int/news/item/27-04-2022-unicef-and-who-warn-of--perfect-storm--of-conditions-for-measles-outbreaks--affecting-children.
15) Atkinson J, Salmond C, Crampton P. NZDep2018 Index of Deprivation, Final Research Report. Department of Public Health, University of Otago, Wellington. December 2020.
16) Ministry of Health – Manatū Hauora [Internet]. Measles and Rubella Elimination in New Zealand, 2021 - Report to the 8th Meeting of the Western Pacific Regional Verification Commission for Measles and Rubella Elimination, 2021. Wellington, New Zealand; 2021.
17) World Health Organization. Global Health Observatory - Measles-containing-vaccine first-dose (MCV1) immunization coverage among 1-year-olds. [Updated 2022; cited 2022 Aug 29.] Available from: https://www.who.int/data/gho/data/indicators/indicator-details/GHO/measles-containing-vaccine-first-dose-(mcv1)-immunization-coverage-among-1-year-olds-(-).
18) Hayman DTS, Marshall JC, French NP, Carpenter TE, Roberts MG, Kiedrzynski T. Global importation and population risk factors for measles in New Zealand: a case study for highly immunized populations. Epidemiol Infect. 2017;145:1875-85.
19) Causey K, Fullman N, Sorensen RJD, et al. Estimating global and regional disruptions to routine childhood vaccine coverage during the COVID-19 pandemic in 2020: a modelling study. Lancet. 2021;398(10299):522-34.
20) Allen + Clarke [Internet]. Improving New Zealand’s childhood immunisation rates. Wellington; 2019. Available from: https://www.health.govt.nz/publication/improving-new-zealands-childhood-immunisation-rates.
21) Pal M, Goodyear-Smith F, Exeter D. Factors contributing to high immunisation coverage among New Zealand Asians. J Prim Health Care. 2014;6(4):304-11.
22) Mills C, Penney L. The Northland emergency meningococcal C vaccination programme. N Z Med J. 2013;126(1373):30-9.
23) Petousis-Harris H, Goodyear-Smith F, Turner N, Soe B. Family physician perspectives on barriers to childhood immunisation. Vaccine. 2004;22(17-18):2340-4.
24) Lee CHJ, Sibley CG. Attitudes toward vaccinations are becoming more polarized in New Zealand: Findings from a longitudinal survey. EClinicalMedicine. 2020;23.
25) Howe AS, Chisholm H, Paynter J, Willing E, Turner N. Does the National Immunisation Register stack up? Quantifying accuracy when compared to parent-held health record books. N Z Med J. 2021;134 (1541):22-32.
Contact diana@nzma.org.nz
for the PDF of this article
Gaps in measles immunisation coverage for pre-school children in Aotearoa New Zealand: a cross-sectional study
Aotearoa New Zealand has notable immunity gaps in the population and the measles immunisation coverage target of ≥95% to prevent measles transmission has not yet been reached.
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