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

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.
Competing Interests: Potential conflicts of interest. H. B. received lecture fee from BMS. F. F. received research grants from the Novo Nordisk Foundation and the Laerdal Foundation. M. G.-B. reports working as an unpaid chairman for the Committee for Transfusion Medicine, Danish Society for Clinical Immunology. A. D. K. received a research grant from the Danish Heart Foundation. T. B. reports grants for his institution from the Novo Nordisk Foundation, Simonsen Foundation, Lundbeck Foundation, Kai Foundation, and Erik and Susanna Olesen’s Charitable Fund. T. B. also reports the following: an unrestricted grant for his institution and working on the advisory board for GSK; an unrestricted grant for his institution, working as a principal investigator for a clinical trial, and working on the advisory board for Pfizer; working as a principal investigator for a clinical trial for Boehringer Ingelheim; an unrestricted grant for his institution, working as a principal investigator for a clinical trial, and working on the advisory board for Gilead Sciences; an unrestricted grant for his institution, working as a principal investigator, and working on the advisory board for MSD; working as a board member for Pentabase; working as a principal investigator for clinical trials for Roche, Novartis, and Kancera AB; and working on the advisory board for Janssen and Astra Zeneca. T. B. received consulting fees from GSK and Pfizer. T. B. held lectures for GSK, Pfizer, Gilead Sciences, Boehringer Ingelheim, Abbvie, and Astra Zeneca. T. B. received a donation of trial medication from Eli Lilly. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
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