BCG-induced trained immunity on clinical outcomes in moderate to severe COVID-19 patients at a tertiary care center: A comparative study based on interferon-gamma release assays status.

BACKGROUND: (BCG) Bacillus Calmette-Guérin-induced trained immunity has enhanced non-specific protection against a range of pathogens, boosting the immune system's ability to respond to infections beyond its primary target, tuberculosis. This study explores the effect of indirect immunity by BCG vaccine as ascertained by interferon-gamma release assays (IGRA) values and clinical outcomes in COVID-19 patients. METHODS: A purposive sampling of 110 severe and moderate COVID-19 patients admitted to a Tertiary care center, Rajasthan was conducted. QuantiFERON-TB (QFT) tests were applied to measure IGRA levels in the blood sample. Clinical outcomes like the length of hospital stay and in-hospital mortality were studied. Mann-Whitney and Fischer's Exact Tests were used to determine the significance of the association using P-values. RESULTS: A total of 13 out of 110 individuals were found to be IGRA positive. The age difference between the two groups was not significant. Most of the patients, who tested negative on the IGRA test were male (90.2%). There was a significant difference in the duration of hospital stay between the two groups (IGRA positive (2-11 days); IGRA negative (7-16 days); and P = 0.049). CONCLUSION: BCG-induced trained immunity shortens the duration of hospital stay in COVID-19 affected individuals. More studies on cross-protection offered by BCG vaccines may help understand the potential role of trained immunity in reducing the severity and spread of other viral infections, including COVID-19. This research could have significant implications for public health strategies and the development of novel vaccination approaches to combat infectious diseases more effectively.