Herd Immunity in Influenza
Mark Loeb and colleagues have produced another fine study. They report in JAMA the results of a cluster-randomized trial where they vaccinated children aged 3-15 in 49 small communities in rural Canada. Children were vaccinated with either inactivated trivalent influenza vaccine or hepatitis A vaccine as a control. Confirmed influenza (RT-PCR) was 61% lower in non-recipients in the communities where children were vaccinated (3.1%) compared to non-recipients in unvaccinated communities (7.6%). Their main conclusion was that "a significant herd immunity effect can be achieved when the uptake of vaccine is approximately 80% in clusters in which children and adolescents aged 3 to 15 years are immunized." One note: this study was completed during the 2008-2009 season.