Does prior vaccination affect the immune response to seasonal influenza vaccination among older adults? Findings from a prospective cohort study in a Northeastern Province of Thailand.

Abstract

BackgroundWe measured the immunogenicity of seasonal trivalent inactivated influenza vaccines (IIV3) among older Thai adults and the effect of one-year prior vaccination status on immune responses.MethodAdults aged ≥65 years (n = 370) were vaccinated with Southern Hemisphere IIV3 in 2015. Hemagglutination inhibition assays were performed using goose red blood cells on sera collected from the participants at baseline and after 1, 6, and 12 months of vaccination. Prior year vaccination (in 2014) was verified with the national health security office database. We analyzed the associations between prior vaccination and geometric mean titers (GMT) at each time point using generalized linear regression on logged transformed titers, and seroprotection and seroconversion using Log-binomial regression.ResultsAt baseline, previously vaccinated participants (n = 203) had a significantly higher GMT and seroprotection against all three influenza strains than those previously unvaccinated (n = 167) (all p-values ConclusionInfluenza vaccination elicited good humoral response in older Thai adults. While seroconversion seemed attenuated in persons previously vaccinated for influenza A(H1N1)pdm09 (the only vaccine strain not to change), this was not apparent for influenza A(H3N2) and B, and prior vaccination was not associated with any inhibition in seroprotection.