Humoral immunity in elderly people vaccinated against influenza on the eve of the cancellation of the COVID-19 pandemic status

Abstract

Introduction. According to the United Nations Population Division, by 2050, 25% of the population will be over 65 years of age due to increasing life expectancy. Influenza-related morbidity and mortality are disproportionately high among older people. In the WHO European Region in 2004–2017, the highest proportion of influenza A(H3N2) virus was observed in the age group ≥ 65 years — 10%. The effectiveness of influenza vaccination decreases in individuals over 65–70 years of age due to age-related immune dysfunction (immunosenescence). The decrease in influenza vaccine effectiveness with age may be associated with an imbalance in effector memory T cells and regulatory responses. In the United States, high-dose or adjuvanted influenza vaccines are recommended in preference to standard-dose non-adjuvanted influenza vaccines for individuals aged 65 years and older. In this age group, these vaccines are potentially more effective in terms of hospitalizations and economically than non-adjuvanted influenza vaccines in standard doses. The aim of this study was to investigate the ability to form a protective titer of antibodies to influenza virus strains included in the vaccine at the end of the COVID-19 pandemic in the elderly. Materials and methods. A total of 31 participants over 60 years of age took part in the study, who were immunized with an influenza quadrivalent inactivated subunit adjuvant vaccine by intramuscular administration. Antibodies to influenza virus strains were determined by performing a hemagglutination inhibition (HI) test one month after administration. Results. For individuals over 60 years old, 1 month after vaccination, a statistically significant increase in the seroprotection level (p < 0.05) is observed in relation to three strains: A/Victoria/2570/2019(H1N1) pdm09 up to 74.2%, A/H3N2/Darwin/9/2021 up to 93.2% and B/Austria/1359417/2021 up to 74.2%. The seroprotection level to the B/Phuket/3073/13 strain was 35.5%. The geometric mean antibody titer (GMT) of individuals in the older age group before vaccination for the H1N1 strain was 15.1 (log2 3.91 ± 0.59), after vaccination – 73.7 (log2 6.20 ± 0.93); for the H3N2 strain – 52.7 (log2 5.72 ± 0.97) and 147.4 (log2 7.20 ± 1.22) before and after, respectively; for the B/Yamagata strain – 8.6 (log2 3.11 ± 0.54) and 24.1 (log2 4.59 ± 0.79) before and after, respectively; for the B/Victoria strain, the GMT was 10.1 (log2 3.33 ± 0.38), after – 63.0 (log2 5.98 ± 0.69). The seroconversion rate (SCR) significantly exceeded the required level of 2.00 for all strains (p < 0.05). For both H3N2 and B/Yamagata strains, the GMT was 2.8, for H1N1 and B/Victoria strains – 4.89 and 6.26, respectively. The seroconversion rate for H3N2 and B/Yamagata strains was 41.9%, for the H1N1 strain – 61.3%, for the B/Victoria strain – 77.4%. Conclusion. The immunogenicity of each component of the influenza vaccine in a single intramuscular immunization of volunteers over 60 years old met at least one criterion of the requirements for inactivated influenza vaccines.

Keywords

• influenza
• adjuvanted influenza vaccine
• immunogenicity
• vaccine effectiveness
• safety
• covid-19