Influenza vaccination influencing level of specific humoral immunity in healthy individuals

Abstract

To assess an effect of vaccination on the level of humoral anti-influenza herd immunity, 2955 sera were collected and analyzed by HIT in the 2019–2020 and 2020–2021 epidemiological seasons. All sera were obtained from healthy adult donors residing in various cities of the Russian Federation. Among them, 1057 volunteers were vaccinated with seasonal influenza trivalent inactivated vaccine. Characteristics of humoral anti-influenza immunity (average geometric antibody titers and the proportion of individuals seropositive for the vaccine viruses) obtained in autumn 2019 and 2020 (1–2 months after vaccination) in vaccinated individuals vs. unvaccinated subjects were found to be markedly higher evidencing about a positive vaccination-related contribution to developing herd immunity against influenza in the preepidemic periods. After the 2019–2020 influenza epidemic, in spring 2020 (6–7 months after vaccination), the levels of antibodies to all vaccine components decreased by 2.6–3.5-fold in vaccinated donors compared to the pre-epidemic period in 2019 autumn. Antibody titers became substantially lower than the protective level (titer by HIT 1/40). At the same time, no significant differences between the groups of vaccinated vs. unvaccinated individuals were observed afterwards. This indicates instability of post-vaccination anti-influenza humoral immunity. As a result, it may decrease an influenza-resistant population cohort of working age on the eve of new epidemic season. The immunogenicity of the inactivated trivalent seasonal influenza vaccine was estimated by HIT while analyzing paired sera obtained from 295 and 112 healthy individuals of various ages vaccinated in autumn 2019 and 2020, respectively. The response to the vaccine was found to be age-related. Children aged 3–14 years vs. older subjects showed a more efficient response. Insufficient immunogenicity of influenza B virus vaccine components was shown. In all age groups, average geometric titers for influenza B virus antibodies were lower (2–8-fold) than for current A(H1N1)pdm09-like strains and influenza A(H3N2) viruses 1–1.5 months post-vaccination. Analyzing vaccine immunogenicity showed a significant inverse relationship between the level of preexisting strain-specific serum antibodies before vaccination and formation of antibodies to the corresponding vaccine virus 1–1.5 months after vaccination. Seroconversion to each vaccine component was remarkably more frequent in individuals with a low preexisting level of antibodies specific to the corresponding virus.