Ensemble model estimates of the global burden of measles morbidity and mortality from 2000 to 2019: a modeling study

Background Measles remains a significant source of childhood morbidity and mortality worldwide. Two doses of measles containing vaccine are recommended for all children and delivered through a combination of routine and supplemental immunization activities. Uncertainty about the degree to which second dose opportunities reach previously unvaccinated children presents a challenge in the assessment of vaccination programs and the estimation of the global burden of measles disease and mortality. Methods We fit an ensemble of models that represent alternative assumptions about the degree to which second dose opportunities reach previously unvaccinated children to routine measles surveillance from 100 countries. Using maximum likelihood we selected the best fit model for each country. We compare the resulting estimates of the burden of measles disease and mortality to existing methods for estimating the burden of measles that assume that second dose opportunities are independent of receipt of the first dose. Findings We find that 78 of 100 countries are best-fit by a model that assumes that second doses that are delivered through supplemental campaigns are preferentially delivered to children who have received a first dose. Using a country-specific best-fit model we estimate that measles mortality has declined by 73% from 2000-2019 compared to an estimated decline of 83% using an assumption of independent doses in all countries. Interpretation Despite large decreases in measles cases over the last two decades, the observed trajectories in most countries suggest that supplemental immunization activities are disproportionately reaching previously vaccinated children. To accelerate measles reduction goals efforts to reach unvaccinated children through supplemental activities and second dose opportunities should be intensified. Funding Bill and Melinda Gates Foundation, World Health Organization