Evaluating effective measles vaccine coverage in the Malaysian population accounting for between-dose correlation and vaccine efficacy

Abstract

Abstract Background Malaysia introduced the double dose measles-mumps-rubella (MMR) vaccine in 2004 as part of its measles elimination strategy. However, despite high historical coverage of first- and second-dose measles-containing vaccine, Malaysia continues to report high measles incidence. This study suggests a novel indicator for investigating population immunity against measles in the Malaysian population. Methods We define effective vaccine coverage (EVC) of measles as the proportion of a population vaccinated with measles-containing vaccine (MCV) and effectively protected against measles infection. A quantitative evaluation of EVC throughout the life course of Malaysian birth cohorts was conducted accounting for both vaccine efficacy (VE) and between-dose correlation (BdC). Measles vaccination coverage was sourced from WHO-UNICEF estimates of Malaysia’s routine immunisation coverage and supplementary immunisation activities (SIAs). United Nations World population estimates and projections (UNWPP) provided birth cohort sizes stratified by age and year. A stepwise joint Bernoulli distribution was used to proportionate the Malaysian population born between 1982, the first year of Malaysia’s measles vaccination programme, and 2021, into individuals who received zero dose, one dose and multiple doses of measles-containing vaccine. Vaccine efficacy estimates by age and doses received are then adopted to derive effective vaccine coverage. A sensitivity analysis was conducted using 1000 random combinations of between-dose correlation and vaccine efficacy parameters. Results This study suggests that no birth cohort in the Malaysian population has achieved > 95% population immunity (EVC) conferred through measles vaccination since the measles immunisation programme began in Malaysia. Conclusion The persistence of measles in Malaysia is due to pockets of insufficient vaccination coverage against measles in the population.Monitoring between-dose correlation through immunisation surveillance systems may allow for the identification of susceptible subpopulations (primarily zero-dose MCV individuals) and increase the coverage of individuals who are vaccinated with multiple doses of MCV. This study provides a tool for assessment of national-level population immunity of measles conferred through vaccination and does not consider subnational heterogeneity or vaccine waning. This tool can be readily applied to other regions and vaccine-preventable diseases.