A systematic review including 10 RCTs with a total of 252 119 subjects was abstracted in DARE. In 3 of the 10 trials, the relative risk increased by 1–18% per year (corresponding to increased efficacy), in the remaining 7 trials the RR decreased by 5–14% per year (corresponding to decreased efficacy). In trials of efficacy 10 years after vaccination, the average efficacy over all the trials was 14% (95% CI -9% to 32%) using a random effects model, and 12% (95% CI -5% to 27%) using a fixed effects model.
Health Technol Assessment evaluated the duration of protection of infant and school-age BCG vaccination in United Kingdom using 2 case-control studies. In the infant BCG study, a protective effect was seen up to 10 years following infant vaccination [< 5 years since vaccination: vaccine effectiveness (VE) 66%, 95% CI 17% to 86%; 5-10 years since vaccination: VE 75%, 95% CI 43% to 89%], but there was weak evidence of an effect 10-15 years after vaccination (VE 36%, 95% CI negative to 77%; p = 0.396). For school-aged BCG vaccination, VE was 51% (95% CI 21% to 69%) 10-15 years after vaccination and 57% (95% CI 33% to 72%) 15-20 years after vaccination, beyond which time protection appeared to wane. Ascertainment of vaccination status was based on self-reported history and scar reading.
Comment: The quality of evidence is downgraded by inconsistency of results and limitations of review methdology.