Accepted for/Published in: JMIR Public Health and Surveillance
Date Submitted: Jan 25, 2022
Date Accepted: Oct 18, 2022
Date Submitted to PubMed: Oct 20, 2022
Warning: This is an author submission that is not peer-reviewed or edited. Preprints - unless they show as "accepted" - should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information.
Outcomes of the COVID-19 infection in people previously vaccinated against influenza. A population-based cohort study with electronic health records.
ABSTRACT
Background:
A possible link between influenza immunization and susceptibility to COVID-19 infection has been previously suggested due to a boost in the immunity against SARS-CoV-2.
Objective:
We aimed to assess this hypothetic association in our setting.
Methods:
Population-based cohort study including all patients with COVID-19 registers in the primary health care (PHC) electronic records during the first wave of the COVID-19 pandemic (1st March 2020 – 30th June 2020) in Catalonia, Spain. We compared those people ever exposed to influenza vaccine before the COVID-19 infection with those never exposed. The data source is SIDIAP, capturing PHC information of 5.8 million people from Catalonia. The main outcomes assessed during follow-up were diagnosis of pneumonia, hospital admission and mortality.
Results:
We included 309,039 COVID-19 patients and compared them according to their influenza immunization status, being 114,181 (36.9%) vaccinated at least once and 194,858 (63.1%) never vaccinated. 21,721 (19%) of the flu-vaccinated and 11,000 (5.7%) of the non-vaccinated had at least one of the outcomes assessed. Those vaccinated against flu at any time, recently or recurrently before COVID-19 had higher risk of presenting at least one of the outcomes than those non-vaccinated. When we excluded people living in long-term care facilities, the results were similar.
Conclusions:
We were not able to find a protective role of the immunity conferred by the influenza vaccine on the outcomes of the COVID-19 infection, as the risk of COVID-19 complications was higher in the vaccinated than in the non-vaccinated. Our results are from the first wave of the pandemic, were more complications and mortality due to COVID-19 occurred. Despite that, our study adds more evidence to the analysis of the possible link between the quality of the immunity and the COVID-19 outcomes and to the analysis of PHC patients. Clinical Trial: AEMPS classification IDI-VAC-2020-21. Estudio Posautorización con Otros Diseños diferentes al de seguimiento prospectivo, EPA-OD. 15th September 2020.
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