Bacillus Calmette-Guérin Vaccination and SARS-CoV-2 Infection among Healthcare Workers: A Case-Control Study in Cape Verde

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Introduction: Healthcare workers (HCWs) faced a heightened risk of SARS-CoV-2 infection compared to the general population. The Bacillus Calmette-Guérin (BCG) vaccine, used for over a century, is known to modulate immune responses to various pathogens, including the SARS-CoV-2. This study examines the association between lifetime BCG vaccination and the risk of SARS-CoV-2 infection among HCWs in Cape Verde. Methods: We conducted a case-control study among HCWs in Cape Verde in 2021. Cases were HCWs, 18 years or older who tested positive for SARS-CoV-2 via PCR or Rapid Antigen Test, identified by Public Health Authorities, while controls were HCWs, 18 years or older with no reported or suspected SARS-CoV-2 infection, confirmed by POC Rapid Antigen Test. Both were selected from HCWs of three hospitals on Santiago and São Vicente islands in Cape Verde. The primary outcome measured was the status of SARS-CoV-2 infection (yes/no), and the primary exposure examined was BCG vaccination status (yes/no). The study also considered sociodemographic, epidemiological, and employment variables. Data collection was conducted using an electronic questionnaire applied to all participants, and analysis employed a maximum likelihood forward selection logistic regression model to assess the impact of BCG vaccination on the odds of SARS-CoV-2 infection. Results: The study included 215 cases and 250 controls. Most cases of SARS-CoV-2 infection that occurred before completion of COVID-19 vaccination were identified through epidemiological surveillance or among people who reported being quarantined and/or absent from work after diagnosis. Hospitalization for COVID-19 was required for 7.7% of the cases. Persistent symptoms following COVID-19 were reported in fewer than 1% of cases. Having at least one child in the house, not having double employment, and being of normal weight were more likely to be observed among cases than controls. BCG vaccination showed no association with SARS-CoV-2 infection (aOR of BCG-vaccinated vs. not BCG-vaccinated = 0.76 [0.48; 1.20]). Completing the COVID-19 vaccination regimen was associated with reduced odds of SARS-CoV-2 infection, but there was likely some reversed causation, as vaccination was postponed for 6 months post-COVID-19 infection for cases. Conclusions: Lifetime BCG vaccination did not reduce the likelihood of SARS-CoV-2 infection among HCWs.

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