Correlates of immune protection induced by live, attenuated, cold-adapted,trivalent, intranasal influenza virus vaccine

The authors conducted a 2-year, multicenter, double-blind, placebo-controll ed efficacy field trial of live, attenuated, cold-adapted, trivalent influe nza vaccine administered by nasal spray to children 15-71 months old. Overa ll, vaccine was 92% efficacious at preventing culture-confirmed infection b y influenza A/H3N2 and influenza B, Because influenza A/H1N1 did not cause disease during the years in which this study was conducted, the authors sou ght to determine vaccine efficacy and correlates of immune protection again st experimental challenge with 10(7) TCID50 of attenuated H1N1 (vaccine str ain) by intranasal spray. Prechallenge assessments included serum hemagluti nation-inhibiting (HAI) antibody and nasal wash IgA antibody to H1N1, Vacci ne was 83% efficacious (95% confidence interval, 60%-93%) at preventing she dding of H1N1 virus after challenge. Any serum HAI antibody or any nasal wa sh IgA antibody was correlated with significant protection from H1N1 infect ion as indicated by vaccine-virus shedding, and high efficacy against H1N1 challenge was demonstrated.