• Susan Martins Pereira, Florisneide Rodrigues Barreto, Ramon Andrade de Souza, Carlos Antonio de Souza Teles Santos, Marcos Pereira, Enny Santos da Paixão, Carla Cristina Oliveira de Jesus Lima, Marcio Santos da Natividade, Ana Angélica Bulcão Portela Lindoso, Eder Gatti Fernandes, Evonio Barros Campelo Junior, Julia Moreira Pescarini, Kaio Vinicius Freitas de Andrade, Fernanda Mattos de Souza, Elisangela Alves de Britto, Ceuci Nunes, Maria Yuri Ichihara, Margareth Dalcolmo, Anete Trajman, Manoel Barral-Netto, Ibrahim Abubakar, Mauricio Lima Barreto, Ricardo Arraes de Alencar Ximenes, and Laura Cunha Rodrigues.
• Institute of Collective Health, Federal University of Bahia, Salvador, Brazil.
• Bmc Med. 2023 Apr 13; 21 (1): 145145.

BackgroundBCG vaccination, originally used to prevent tuberculosis, is known to "train" the immune system to improve defence against viral respiratory infections. We investigated whether a previous BCG vaccination is associated with less severe clinical progression of COVID-19 METHODS: A case-control study comparing the proportion with a BCG vaccine scar (indicating previous vaccination) in cases and controls presenting with COVID-19 to health units in Brazil. Cases were subjects with severe COVID-19 (O2 saturation < 90%, severe respiratory effort, severe pneumonia, severe acute respiratory syndrome, sepsis, and septic shock). Controls had COVID-19 not meeting the definition of "severe" above. Unconditional regression was used to estimate vaccine protection against clinical progression to severe disease, with strict control for age, comorbidity, sex, educational level, race/colour, and municipality. Internal matching and conditional regression were used for sensitivity analysis.ResultsBCG was associated with high protection against COVID-19 clinical progression, over 87% (95% CI 74-93%) in subjects aged 60 or less and 35% (95% CI - 44-71%) in older subjects.ConclusionsThis protection may be relevant for public health in settings where COVID-19 vaccine coverage is still low and may have implications for research to identify vaccine candidates for COVID-19 that are broadly protective against mortality from future variants. Further research into the immunomodulatory effects of BCG may inform COVID-19 therapeutic research.© 2023. The Author(s).

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