BCG Revaccination Fails to Prevent TB Infection in Adolescents
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Reviewed by Dat Tien Nguyen, B.A, ScM.
Translated by Nhi Phuong Quynh Le, B.A |
Posted on June 2nd, 2025
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Tuberculosis continues to pose a major public health burden in Vietnam and around the world, causing over 1 million deaths annually. Although the bacille Calmette–Guérin (BCG) vaccine has been used for decades to prevent infection, its protective effect diminishes over time. There has been growing interest in exploring whether revaccination with BCG could restore immunity. With support from the Bill & Melinda Gates Foundation, a study was conducted to evaluate the impact of BCG revaccination on tuberculosis prevention.
The phase 2 clinical trial was carried out in South Africa and enrolled 1,836 HIV-negative adolescents aged 10 to 18 who tested negative for Mycobacterium tuberculosis using the QuantiFERON-TB assay. Participants were randomly assigned to receive either the BCG vaccine or a placebo. Seventy-one days after vaccination, the researchers observed an increase in antigen-specific CD4+ T cells and a higher frequency of cytokine-producing CD4+ lymphocytes in the BCG group. Despite this immunologic response, BCG revaccination did not lead to a reduced risk of infection. This finding contrasts with earlier research that suggested a 45.4% efficacy rate. The discrepancy was not attributable to differences in vaccine strain or case definition. Instead, the variation may stem from broader participant demographics, the use of a different QuantiFERON-TB assay, or — most plausibly — reduced tuberculosis transmission during COVID-19 lockdowns, which likely suppressed infection rates in the placebo group as well.
The phase 2 clinical trial was carried out in South Africa and enrolled 1,836 HIV-negative adolescents aged 10 to 18 who tested negative for Mycobacterium tuberculosis using the QuantiFERON-TB assay. Participants were randomly assigned to receive either the BCG vaccine or a placebo. Seventy-one days after vaccination, the researchers observed an increase in antigen-specific CD4+ T cells and a higher frequency of cytokine-producing CD4+ lymphocytes in the BCG group. Despite this immunologic response, BCG revaccination did not lead to a reduced risk of infection. This finding contrasts with earlier research that suggested a 45.4% efficacy rate. The discrepancy was not attributable to differences in vaccine strain or case definition. Instead, the variation may stem from broader participant demographics, the use of a different QuantiFERON-TB assay, or — most plausibly — reduced tuberculosis transmission during COVID-19 lockdowns, which likely suppressed infection rates in the placebo group as well.