The safety of BCG revaccination: A systematic review.

Introduction: Revaccination with Bacillus Calmette-Guérin (BCG) vaccine is not generally recommended due to a lack of proven efficacy of repeat doses for protection against tuberculosis. However, there is a growing interest in the use of BCG vaccine for its 'off-target' effects which might involve revaccination. We did a systematic review of the safety of BCG revaccination.

Methods: MEDLINE (1946 to March 2020) and the BCG World Atlas (updated 2017) were searched, limiting to studies of BCG administration by the intradermal or percutaneous route. Adverse events as well as patient and vaccine characteristics were reviewed.

Results: The search identified 388 articles, of which 24 met the inclusion criteria. These reported 22 studies comprising eight randomised trials, four case-control studies, four observational studies and six case series or reports. Overall, there was evidence for a small increase in the rate of mild local and systemic reactions. No serious adverse events were reported in immunocompetent individuals.

Conclusions: Evidence to date suggests that revaccination with BCG vaccine carries minimal risk. Future studies of BCG vaccine for novel applications should report adverse event data stratified by prior BCG vaccination status.