This “Uncertainties” article forms one of a series of occasional articles published in the BMJ that highlight areas of practice where management lacks convincing supporting evidence. The current article focuses on the uncertainties around the duration of protection provided by BCG vaccination. The authors note that universal BCG vaccination of school children with a negative tuberculin skin test was discontinued in 2005. The authors add that this uncertainty has implications for the cost effectiveness of vaccination at later ages and for the role of a new vaccine.

In discussing how best to deal with the uncertainty, the authors write, “The best estimate of duration of protection by BCG is currently about 10 years, with recent data suggesting that the vaccine may protect for longer, although the level of protection seems to fall with time. People vaccinated 10 years or more before coming into close contact with infectious tuberculosis might have no BCG derived protection against active disease. BCG does not protect when given to people who are already infected, and revaccination of individuals after initial vaccination does not seem to offer substantial additional protection. We therefore do not recommend repeat vaccination, even in people travelling to countries with a high tuberculosis burden.”