Effect of Influenza Vaccination on Risk of Coronavirus Disease 2019: A Prospective Cohort Study of 46 000 Healthcare Workers

Abstract Background The purpose of this study was to assess whether influenza vaccination has an impact on the risk of coronavirus disease 2019 (COVID-19). Methods A cohort of 46 112 healthcare workers were tested for antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and filled in a survey on COVID-19 symptoms, hospitalization, and influenza vaccination. Results The risk ratio of hospitalization due to SARS-CoV-2 for influenza vaccinated compared with unvaccinated participants was 1.00 for the seasonal vaccination in 2019/2020 (confidence interval, .56–1.78, P = 1.00). Likewise, no clinical effect of influenza vaccination on development of antibodies against SARS-CoV-2 was found. Conclusions The present findings indicate that influenza vaccination does not affect the risk of SARS-CoV-2 infection or COVID-19. This cohort study of 46 112 healthcare workers examined the effect of influenza vaccination on hospitalization and symptoms due to COVID-19 and development of antibodies against SARS-CoV-2. Influenza vaccination had no effect on the specified outcomes.