The determination of haemagglutinin influenza antibodies in the Polish population in the epidemic season 2020/2021 during the SARS-CoV-2 pandemic

The aim of the study was to prove the level of antibod-ies against haemagglutinin in the sera of people from seven age groups in the epidemic season 2020/2021 in Poland to determine the differentiation of the an-tibody level and the protection rate depending on age. The level of anti-haemagglutinin antibodies was established by haemagglutinin inhibition test (HAI). A total of 700 randomly selected sera from people be-longing to 7 different age groups were tested. The re-sults confirmed the presence of antibodies against the following influenza antigens: A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09-like virus, A/ Hong Kong/2671/2019 (H3N2)-like virus, B/Wash-ington/02/2019 (B/Victoria lineage)-like virus and B/ Phuket/3073/2013 (B/Yamagata lineage)-like virus. The level of haemagglutinin antibodies varied between the studied age groups, with the highest values in the 5-9 age group and the lowest in the 0-4 age group. It was also proven that the protection rate was the highest for the A/Hong Kong/2671/2019(H3N2)-like virus antigen, which exceeded the protection level in the 5 age groups. Considering the very low percentage of people vaccinat-ed in the epidemic season 2020/2021 in Poland, which amounted to only 6.1%, the results should be interpret-ed as the immune system's response to an infection with influenza virus.