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Evidence summaries

Does the Efficacy of BCG Vaccine Decline with Time?

The protection given by BCG may wane with time. Published studies do not provide evidence of a protective effect more than 10 years after infant vaccination. Level of evidence: "C"

A systematic review 1 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 2 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.

    References

    • Sterne JA, Rodrigues LC, Guedes IN. Does the efficacy of BCG decline with time since vaccination? Int J Tuberc Lung Dis 1998 Mar;2(3):200-7. [PubMed] [DARE]
    • Mangtani P, Nguipdop-Djomo P, Keogh RH et al. Observational study to estimate the changes in the effectiveness of bacillus Calmette-Guérin (BCG) vaccination with time since vaccination for preventing tuberculosis in the UK. Health Technol Assess 2017;21(39):1-54. [PubMed]

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