Several earlier studies have indicated a favorable effect of flu shots on the risk of infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as well as on the risk of symptomatic and severe coronavirus disease 2019 (COVID-19) after infection. A new preprint reports the effectiveness of influenza vaccination in this light.

Introduction

The influenza vaccine is protective against the influenza virus, reducing the number of cases and deaths that occur with this seasonal pathogen. Flu shots are a high priority for older adults and healthcare workers (HCWs) at a greater risk of infection and complications.

Earlier research suggests a link between SARS-CoV-2 infection/adverse COVID-19 outcomes and prior influenza vaccination. There was a need to make sure that this was not because flu shots are more likely to be taken by the health-conscious, who are also more compliant with protective health behaviors against COVID-19. This is called the healthy user effect and is a potential source of bias in such studies.

The current study, which appears on the medRxiv* preprint server, was performed in Qatar, including over 30,000 healthcare workers vaccinated against influenza during the period between September 17, 2020, and December 31, 2020, when the annual flu shots are usually given. Significantly, this was before the rollout of COVID-19 vaccines.

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