Model-based projections of the population-level impact of hepatitis A vaccination in Mexico

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There are indications of a shift in the pattern of hepatitis A (HAV) in Mexico from high to intermediate endemicity, progressively increasing the mean age of infection and the proportion of cases which are symptomatic. This study estimated the potential impact of universal infant HAV vaccination in Mexico with two doses of Havrix™ at 12 and 18 mo of age on all HAV infections and symptomatic HAV infections. We developed a dynamic transmission model that accounts for changes in demography and HAV epidemiology. It was calibrated using Mexican age-specific seroprevalence and symptomatic HAV incidence data. With 70% first-dose coverage and 85% second-dose coverage, the calibrated model projected that HAV vaccination would reduce the incidence of all HAV infections (symptomatic and asymptomatic) after the first 25 y of vaccination by 71–76% (minimum and maximum for different transmission scenarios). The projected reduction in cumulative incidence of symptomatic HAV infections over the first 25 y of vaccination was 45–51%. With 90% first-dose coverage and 85% second-dose coverage, the projected reduction in incidence of all HAV infections was 85–93%, and the projected reduction in the cumulative incidence of symptomatic HAV infections was 61–67%, over a 25-y time frame. Sensitivity analyses indicated that second-dose coverage is important under the conservative base-case assumptions made about the duration of vaccine protection. The model indicated that universal infant HAV vaccination could substantially reduce the burden of HAV disease in Mexico.