LEVEL OF INFLUENZA VIRUS STRAIN ANTIBODIES IN HEALTHY VACCINATED PEOPLE AT THE END OF THE COVID-19 PANDEMIC; [УРОВЕНЬ АНТИТЕЛ К ШТАММАМ ВИРУСА ГРИППА У ЗДОРОВЫХ ВАКЦИНИРОВАННЫХ НА ЭТАПЕ ЗАВЕРШЕНИЯ ПАНДЕМИИ COVID-19]

Introduction. Abnormally low global influenza detection rates were observed at the peak of ongoing COVID-19 infection. In the 2021–2022 season, influenza resumed circulation, and in December 2022 its incidence rate returned to the 2015–2016 season levels, which exceeded the highest value recorded in 2018 worldwide. There is a need to assess changes in pattern of population immunity after influenza vaccination during the global COVID-19 pandemic. The study was aimed at analyzing level of vaccine influenza virus strain antibodies in healthy people formed during the COVID-19 pandemic. Materials and methods. A total of 123 healthy volunteers immunized with influenza quadrivalent inactivated subunit adjuvanted vaccine and 47 unimmunized volunteers were enrolled in the study. Influenza virus strains antibodies were assessed by performing a hemagglutination inhibition (HI) test one month after vaccination. Results. A significantly increased seroprotection rate (SPR) (p < 0.05) was show in main group that reached 78.9% against the A/Victoria/2570/2019(H1N1)pdm09 strain, 94.3% — against A/H3N2/Darwin strain /9/2021, 69.1% — against B/Phuket/3073/13 strain and 48.8% — against B/Austria/1359417/2021 strain one month after vaccination. The GMT ratio to influenza A(H1N1), B (Victoria) and B (Yamagata) viruses exceeded the required minimum value (p < 0.05) and comprised 4.1 (CI 3.68–4.54), 3.80 (CI 3.33–4.33) and 4.76 (CI 3.87–5.47), respectively. The post-vaccination GMT ratio to influenza A(H3N2) virus was 2.45, which is lower than the required level of 2.50 (p < 0.05). The seroconversion rate (SCR) for strains A/Victoria/2570/2019(H1N1)pdm09, B/ Phuket/3073/2013 and B/Austria/1359417/2021 was 56.1%, 50.4% and 51.2%, respectively. The SCR of the influenza A(H3N2) virus like GMT ratio was minimal among the four strains (p < 0.05) and comprised 38.2%. Conclusion. The vaccine-related immunogenic activity met the requirements for inactivated seasonal influenza vaccines by at least one criterion. © 2024 Saint Petersburg Pasteur Institute. All rights reserved.