BACKGROUND The aim of this study was to determine the level of anti-hemagglutinin antibodies in the serum of recovered patients during the SARS-CoV-2 pandemic in the 2019/2020 epidemic season in Poland, and the course of COVID-19. MATERIAL AND METHODS The material for the study consisted of the sera of COVID-19 convalescents obtained from the following 9 Regional Blood Donation and Blood Supply Centers located in 8 voivodeships. The hemagglutination inhibition reaction assay (HAI) using 8 viral hemagglutination units was used to determine antibody levels, in accordance with WHO recommendations. RESULTS This research confirms that a patient's declared severity of the course of SARS-CoV-2 infection is influenced by the patient's age and concomitant diseases. There was no statistically significant correlation between the level of anti-hemagglutinin antibodies and the severity of the course of a SARS-CoV-2 infection. Based on the serological tests conducted, it can be unequivocally concluded that both vaccinated and influenza-infected patients had a response rate in line with the requirements of the European Commission and the Committee for Medicinal Products for Human Use hemagglutinin antibodies for 4 influenza virus antigens tested. CONCLUSIONS Patients who confirmed their antibody levels with the Commission of the European Communities and the Committee for Propriety Medicinal Products (CPMP) requirements had a mild COVID-19 course. The results of our research emphasize the role of anti-hemagglutinin antibodies in the course of SARS-CoV-2 infection. COVID-19 convalescents have a higher response rate against all 4 types of anti-hemagglutinin antibodies analyzed.