Data from: Influenza hemagglutination-inhibition antibody titer as a mediator of vaccine-induced protection for influenza B

Background: The hemagglutination inhibition (HAI) assay is an established
correlate of protection for the inactivated influenza vaccine, but the
proportion of vaccine-induced protection that is mediated by the
post-vaccination HAI titer has not been assessed. Methods: We used data
from a randomized placebo-controlled trial of a split-virion inactivated
influenza vaccine in children 6-17 years of age. Sera were collected
before and 30 days after receipt of vaccination or placebo, and tested by
the HAI assay against B/Brisbane/60/2008-like (B/Victoria lineage). We
fitted Cox proportional hazards models to the time to laboratory-confirmed
influenza B. We used causal mediation analysis to estimate the proportion
of the total effect of vaccination that was mediated by higher HAI titers.
Results: We estimated that vaccine efficacy against confirmed B/Victoria
infection was 68% (95% CI: 33%, 88%), and post-vaccination HAI titers
explained 57% of the effect of vaccination on protection. Conclusions: The
majority of the effect of inactivated influenza vaccination in children is
mediated by the increased HAI titer after vaccination, but other
components of the immune response to vaccination may also play a role in
protection and should be further explored. Causal mediation analysis
provides a framework to quantify the role of various mediators of
protection.