Efficacy of Live Attenuated Influenza Vaccine Upon Revaccination of Children
Background: Recent observational studies yield conflicting results regarding the effectiveness of repeated influenza vaccination. This meta-analysis evaluates the efficacy of live attenuated influenza vaccine (LAIV) in children upon revaccination. LAIV is approved for children ≥24 months of age.
Methods: All randomized double-blind clinical trials that evaluated the efficacy against laboratory confirmed cases of influenza of LAIV versus placebo in children in 2 consecutive influenza seasons were reviewed. LAIV consisted of 106.5–7.5 median tissue culture infectious doses of each of the 3 influenza strains (A/H1N1, A/H3N2, and B) and was administered as 2 doses in season 1 and 1 dose in season 2.
Results: Four published studies were identified; 6090 children aged 18 months to 7 years in season 2 were included in the analysis. Efficacy in season 2 of LAIV administered over 2 consecutive seasons was 76.7% (95% CI: 71.2%, 81.2%; Fig1A) against all strains and 86.7% (81.5%, 90.5%; Fig1B) against antigenically similar strains. In the absence of revaccination, residual efficacy in season 2 of LAIV administered in the prior season was 40.7% (22.6%, 54.6%) against all strains and 56.4% (37.0%, 69.8%) against antigenically similar strains. Among LAIV recipients in season 1, the additional efficacy of LAIV administered in season 2 was 27.6% (0.8%, 47.2%) against all strains and 58.4% (28.3%, 75.9%) against antigenically similar strains. LAIV administered over 2 consecutive seasons was also compared with LAIV administered in season 2 only: the 2 strategies were equally efficacious against all strains (relative efficacy: 0.0% [-49.1%, 28.5%]); against antigenically similar strains administration over 2 consecutive seasons was more efficacious than administration in season 2 only (relative efficacy: 53.9% [17.4%, 74.3%]).
Conclusion: No reduction in vaccine efficacy was observed with LAIV administered over 2 consecutive seasons, with overall efficacy rates greater than 75%. The efficacy of LAIV over 2 consecutive seasons was also similar to or higher than the efficacy of LAIV administered in season 2 only.
This study was sponsored by MedImmune.
MedImmune: Employee, I am a full time employee of MedImmune and Salary
T. Heikkinen, AstraZeneca/MedImmune: Collaborator, Presentation at ESPID 2012 Congress and Scientific Advisor, Consulting fee and Speaker honorarium
R. B. Belshe, MedImmune: Consultant, Grant Investigator and Scientific Advisor, Consulting fee, Research grant and Speaker honorarium