How Effective is the BCG Vaccine?

Evidence have previously shown variation in the effectiveness of the Bacillus Calmette–Guérin (BCG) vaccine between trials, which calls into question the effectiveness of the BCG Vaccine. ACTnet's Dr James Trauer and Professor Emma McBryde recently tackled this question in a systematic review titled “Timing of Mycobacterium tuberculosis exposure explains variation in BCG effectiveness: a systematic review and meta-analysis” published in Thorax earlier this year. The focus of the study was the reason for the extreme variation in efficacy estimates between trials of BCG?

In 2019, the BCG vaccine global coverage was 88% indicating promising outcomes for future tuberculosis control yet, this review highlights the ineffectiveness of BCG vaccination in high transmission settings where there is repeated Tuberculosis (TB) exposure. The researchers questioned the reason for the extreme variation in efficacy estimates between trials of BCG vaccination and found it was not fully explained by the current accepted hypotheses, such as latitudinal gradient in non- tuberculous mycobacteria exposure. Variation in background intensity of Mycobacterium tuberculosis transmission is able to explain the considerable heterogeneity in the results of trials of BCG vaccination, with sustained protection more evident in settings of declining transmission.

A new framework was proposed designed for understanding the substantial variation in BCG vaccination trial results, with profound implications for understanding BCG’s effects on the global tuberculosis epidemic

You can access the full study here