Indirect Protection from Vaccinating Children against Influenza A Virus Infection in Households

Abstract

Influenza vaccination is an important intervention to prevent influenza virus infection. Our previous analysis suggested that indirect protection is limited in an influenza B epidemic in Hong Kong. We further analyzed six influenza A epidemics to determine such potential. We applied a statistical model to estimate household transmission dynamics in the 3 influenza A(H3N2) and 3 pandemic influenza A(H1N1) epidemics. Then, we estimated the reduction in infection risk among unvaccinated household members when all children in households are vaccinated, with different assumptions on vaccine efficacy (VE). In the optimal scenario that VE was 70%, the reduction to the total probability of infection was only marginal, with relative probabilities ranged from 0.91–0.94 when all children in households were vaccinated because community was by far the main source of infection during the six epidemics in our study. The proportion of cases attributed to household transmission was 10% (95% CrI: 7%, 13%). Individual influenza vaccination is important even when other household members are vaccinated, given the degree of indirect protection is small.

Block the Spread: Barriers to Transmission of Influenza Viruses

“…Despite these uncertainties, high rates of vaccination are thought to reduce community burden of influenza: A retrospective study examining the impact of mandatory influenza vaccination in school-age children in Japan concluded that herd immunity in this age group prevented ∼40,000 deaths annually (148). In another study focused on household transmission, vaccination of one child per household was estimated to bring about a 10-20% reduction in cases (149).…”