BCG, an attenuated strain of Mycobacterium tuberculosis, has been used as a vaccine against tuberculosis for more than 50 years. There is no consensus, however, on the degree of protection it may offer. Antibacterial vaccines, unlike antiviral vaccines, usually produce only relative protection. Therefore, they offer little hope of eradicating a disease, and their usefulness must be judged by the amount of protection conferred v the cost of administration, and the overall resources that exist to limit the spread of a disease must also be considered.
As pointed out by Clemens et al in this issue of The Journal (p 2362), BCG vaccine trials have shown a broad spectrum of effectiveness, all the way from increasing susceptibility to tuberculosis to 80% protection. The eight trials analyzed in this study represent only a small percentage of those that have been conducted throughout the world, but they are the ones that best