Background: Whether vaccinating children with intranasal live attenuated influenza vaccine (LAIV) is more effective than inactivated influenza vaccine (IIV) in providing both direct protection in vaccinated persons and herd protection in unvaccinated persons is uncertain. Hutterite colonies, where members live in close-knit, small rural communities in which influenza virus infection regularly occurs, offer an opportunity to address this question.
Objective: To determine whether vaccinating children and adolescents with LAIV provides better community protection than IIV.
Design: A cluster randomized blinded trial conducted between October 2012 and May 2015 over 3 influenza seasons. (ClinicalTrials.gov: NCT01653015).
Setting: 52 Hutterite colonies in Alberta and Saskatchewan, Canada.
Participants: 1186 Canadian children and adolescents aged 36 months to 15 years who received the study vaccine and 3425 community members who did not.
Intervention: Children were randomly assigned according to community in a blinded manner to receive standard dosing of either trivalent LAIV or trivalent IIV.
Measurements: The primary outcome was reverse transcriptase polymerase chain reaction-confirmed influenza A or B virus in all participants (vaccinated children and persons who did not receive the study vaccine).
Results: Mean vaccine coverage among children in the LAIV group was 76.9% versus 72.3% in the IIV group. Influenza virus infection occurred at a rate of 5.3% (295 of 5560 person-years) in the LAIV group versus 5.2% (304 of 5810 person-years) in the IIV group. The hazard ratio comparing LAIV with IIV for influenza A or B virus was 1.03 (95% CI, 0.85 to 1.24).
Limitation: The study was conducted in Hutterite communities, which may limit generalizability.
Conclusion: Immunizing children with LAIV does not provide better community protection against influenza than IIV.
Primary funding source: The Canadian Institutes for Health Research.