Context: Children and adolescents appear to play an important role in the transmission of influenza. Selectively vaccinating youngsters against influenza may interrupt virus transmission and protect those not immunized.
Objective: To assess whether vaccinating children and adolescents with inactivated influenza vaccine could prevent influenza in other community members.
Design, setting, and participants: A cluster randomized trial involving 947 Canadian children and adolescents aged 36 months to 15 years who received study vaccine and 2326 community members who did not receive the study vaccine in 49 Hutterite colonies in Alberta, Saskatchewan, and Manitoba. Follow-up began December 28, 2008, and ended June 23, 2009.
Intervention: Children were randomly assigned according to community and in a blinded manner to receive standard dosing of either inactivated trivalent influenza vaccine or hepatitis A vaccine, which was used as a control.
Main outcome measures: Confirmed influenza A and B infection using a real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay and by measuring serum hemagglutination inhibition titers.
Results: The mean rate of study vaccine coverage among eligible participants was 83% (range, 53%-100%) for the influenza vaccine colonies and 79% (range, 50%-100%) for the hepatitis A vaccine colonies. Among nonrecipients, 39 of 1271 (3.1%) in the influenza vaccine colonies and 80 of 1055 (7.6%) in the hepatitis A vaccine colonies had influenza illness confirmed by RT-PCR, for a protective effectiveness of 61% (95% confidence interval [CI], 8%-83%; P = .03). Among all study participants (those who were and those who were not vaccinated), 80 of 1773 (4.5%) in the influenza vaccine colonies and 159 of 1500 (10.6%) in the hepatitis A vaccine colonies had influenza illness confirmed by RT-PCR for an overall protective effectiveness of 59% (95% CI, 5%-82%; P = .04). No serious vaccine adverse events were observed.
Conclusion: Immunizing children and adolescents with inactivated influenza vaccine significantly protected unimmunized residents of rural communities against influenza.
Trial registration: clinicaltrials.gov Identifier: NCT00877396.