Objective To estimate associations between trivalent influenza vaccination and COVID-19 mortality as well as severe clinical outcomes among hospitalised patients.
Design Retrospective observational study.
Setting This study was conducted among hospitalised patients with COVID-19 in Brazil.
Participants We analysed all hospitalised patients with COVID-19 with available vaccination information captured in Brazil’s national electronic respiratory infection data system between 1 January 2020 and 23 June 2020.
Main outcome measures The primary outcomes were age-specific mortality rates of hospitalised patients with COVID-19 with and without recent inactivated trivalent influenza vaccination.
Results A total of 53 752 clinically confirmed COVID-19 cases were analysed. Controlling for health facility of treatment, comorbidities as well as an extensive range of sociodemographic factors, patients who received a recent influenza vaccine experienced on average 7% lower odds of needing intensive care treatment (95% CI 0.87 to 0.98), 17% lower odds of requiring invasive respiratory support (95% CI 0.77 to 0.88) and 16% lower odds of death (95% CI 0.78 to 0.90). Protective effects were larger when the vaccine was administered after onset of symptoms as well as among younger patients.
Conclusion Patients with COVID-19 with recent inactivated influenza vaccination experience significantly better health outcomes than non-vaccinated patients in Brazil. Beneficial off-target effects of influenza vaccination through trained innate immune responses seem plausible and need to be further explored. Large-scale promotion of influenza vaccines seems advisable, especially in populations at high risk for severe COVID-19 disease progression.
- infectious disease medicine
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CD and AB are joint senior authors.
Contributors GF, AB, CD and NO-F conceptualised the paper. GF conducted the analysis and created a first draft. All coauthors provided input on the multiple draft versions and approved the final version of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Disclaimer Given that only publicly available and fully de-identified data were used in this research, the project does not classify as human subjects research.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are publicly available at the Brazilian Ministry of Health website.
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