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Background: The BCG (Bacillus Calmette-Guérin) vaccine can induce nonspecific protection against unrelated infections. We aimed to test the effect of BCG on absenteeism and health of Danish health care workers (HCWs) during the coronavirus disease 2019 (COVID-19) pandemic., Methods: A single-blinded randomized controlled trial included 1221 HCWs from 9 Danish hospitals. Participants were randomized 1:1 to standard dose BCG or placebo. Primary outcome was days of unplanned absenteeism. Main secondary outcomes were incidence of COVID-19, all-cause hospitalization, and infectious disease episodes., Results: There was no significant effect of BCG on unplanned absenteeism. Mean number of days absent per 1000 workdays was 20 in the BCG group and 17 in the placebo group (risk ratio, 1.23; 95% credibility interval, 0.98-1.53). BCG had no effect on incidence of COVID-19 or all-cause hospitalization overall. In secondary analyses BCG revaccination was associated with higher COVID-19 incidence (hazard ratio [HR], 2.47; 95% confidence interval [CI], 1.07-5.71), but also reduced risk of hospitalization (HR, 0.28; 95% CI, .09-.86). The incidence of infectious disease episodes was similar between randomization groups (HR, 1.09; 95% CI, .96-1.24)., Conclusions: In this relatively healthy cohort of HCWs, there was no overall effect of BCG on any of the study outcomes., Clinical Trials Registration: NCT0437329 and EU Clinical Trials Register (EudraCT number 2020-001888-90)., Competing Interests: Potential conflicts of interests . T. B. reports grants or contracts from Novo Nordisk, Simonsen, Lundbeck, Kai, Erik and Susanna Olesen's Charitable Found, GSK, Pfizer, Boehringer Ingelheim, Gilead Sciences, MSD, Pentabase, Roche, Novartis, Kancera AB, Janssen, and Astra Zeneca; consulting fees from GSK and Pfizer; honoraria for lectures from GSK, Pfizer, Gilead Sciences, Boehringer Ingelheim, Abbvie, and Astra Zeneca; and donation of trial medication from Eli Lilly. P. E. K. reports participation on Data Safety Monitoring Board or Advisory Board on trials “Specific and non-specific effects of measles and BCG vaccines for mother and child (MATVAC)”, “Evaluating the effectiveness of different BCG strains in Guinea-Bissau: A randomized trial of the impact on neonatal hospital admissions”, and “BCG vaccine to reduce unplanned absenteeism due to COVID-19 illness of health care workers in Guinea-Bissau and Mozambique. A multi-center single-blinded randomized controlled trial (BCG-COVID-RCT)”, and “A randomized trial of providing BCG vaccination immediately to neonates admitted to the intensive care unit in Guinea-Bissau: Effect on mortality”. C. W. reports honoraria for a lecture from Novartis; and participation on the Advisory Board on COVID-19 Treatments, Danish government. I. S. J. reports honoraria from Pfizer for being chairman for the European Congress of Clinical Microbiology and Infectious Diseases 2023 COVID-19 symposium. M. G. N. reports to be scientific founder and have stock in TTxD and Lemba. All other authors report no potential conflicts. 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., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

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., (© The Author(s) 2022. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)