Vaccinate Now, Pay Later: Effect of Intensive Strain-Matched Vaccination on Seasonal and Pandemic Influenza Epidemic Sizes

Abstract

Pandemic influenza represents a significant public health challenge, as antigenic shift can result in pandemic strains antigenically distinct from strains targeted by earlier strain-matched vaccines,leaving large segments of the population vulnerable to infection. Recent experimental studies have suggested that infection with prior seasonal strains of influenza may provide individuals with short-term transmission-blocking immunity during a pandemic. Given the occurrence of that phenomenon, our model confirms that extensive use of a strain-matched vaccine can result in decreased seasonal epidemic sizes at the expense of increased pandemic sizes. Utilizing a transmission-blocking cross-protective vaccine in conjunction with or lieu of a strain-matched vaccine successfully eliminates this trade-off by reducing both seasonal epidemic and pandemic sizes. Utilizing such a cross-protective vaccine in lieu of a traditional strain-matched vaccine does not result in a trade-off and reduces both seasonal and pandemic sizes. The duration of cross-protective immunity and the frequency of cross-protective vaccination appeared to influence whether sole utilization of cross-protective vaccination resulted in a larger decrease in seasonal epidemic sizes than strain-matched vaccination at a constant vaccine coverage and efficacy. If the half-life is greater than twice the cross-protective vaccination interval, cross-protective vaccination results in a larger decrease in seasonal epidemic sizes compared to equivalent strain-matched vaccination. However, if the half-life is less than the cross-protective vaccination interval, cross-protective vaccination results in a smaller decrease in seasonal epidemic sizes compared to equivalent strain-matched vaccination.