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Epidemiol Infect. 2016 Oct 20:1-9. [Epub ahead of print]
McKEE A1 Shea K1 Ferrari MJ1.
Measles was eliminated in the Americas in 2002 by a combination of routine immunizations and supplementary immunization activities. Recent outbreaks underscore the importance of reconsidering vaccine policy in order to maintain elimination. We constructed an age-structured dynamical model for the distribution of immunity in a population with routine immunization and without disease and analyzed the steady state for an idealized age structure and for real age structures of countries in the Americas. We compared the level of immunity maintained by current policy in these countries to the level maintainable by an optimal policy. The optimal age target for the first routine dose of measles vaccine depends on the timing and coverage of both doses. Similarly the optimal age target for the second dose of measles vaccine depends on the timing and coverage of the first dose. The age targets for the first and second doses of measles vaccine should be adjusted for the post-elimination era by specifically accounting for current context including realized coverage of both doses and altered maternal immunity. Doing so can greatly improve the proportion immune within a population and therefore the chances of maintaining measles elimination without changing coverage.