Is there any effect of flu vaccine on the SARS-CoV-2 infected patients?

OBJECTIVES: On 11 March, WHO declared a global pandemic caused by a new virus of the family Coronaviridae that has since been called SARS-CoV-2. COVID-19 does not have specific antiviral drug treatment currently. There are currently more than one hundred research projects into vaccines against SARS-CoV-2 worldwide, and 17 of them are already being tested on humans, according to the WHO. Until we have an effective vaccine, the possible preventive effect of flu vaccine for SARS-CoV-2 infection based on cross-reactivity has been postulated. Our objective was to analyse the effect of vaccination against flu virus in the season prior to the COVID-19 pandemic in our hospitalized SARS-CoV-2 infected patients. METHODS: We performed a retrospective observational cohort study of patients admitted to hospital with SARS-CoV2 infection. We analysed the differences between patients who had received or had not the flu vaccination for the 2019–2020 season. RESULTS: We found no significant differences (p = 0.09) in patients who died (43 in total), of whom 23 (21.5%) were vaccinated against the flu and 20 (13.5%) were not. In mortality, we obtained an adjusted OR = 0.873 (95% CI: 0.294–2.083), and about the success of health care the adjusted OR was 1.447 (95% CI: 0.610–3.430). CONCLUSIONS: Flu vaccination in patients admitted for SARS-CoV-2 infection had neither a beneficial nor a harmful effect on the clinical courses or outcomes of patients admitted to an European hospital.