051 - Canadian Experience with BCG Vaccine

The BCG (or Bacillus Calmette-Guérin) vaccine (mentioned in 036) is an attenuated strain of Mycobacterium that seemed to work to immunize against tuberculosis, so it's pretty important, but people have always wondered about its effectiveness.

This publication was a short report about BCG usage in Canada, regarding the conclusions of a subcommittee evaluating the value of the vaccine. It claimed that in general, English-speakers (as opposed to, I suppose, French-speakers such as Dr. Calmette) were less optimistic about the vaccine.

However, there had been an 8-year study with 5,126 subjects in Montreal using the BCG vaccine. 582 of the vaccinated subjects had been exposed to tuberculosis from their family situations (not intentionally, of course), and another 500 unvaccinated controls in similar conditions had been exposed. These subjects were 1 month up to 7 years of age; those who died before reaching a month old were excluded because there were too many other causes of death in those, I think.

So overall, about 10 from every 100 of the vaccinated subjects died from any cause, while almost 20 from every 100 died of the unvaccinated. In the vaccinated, about 2 of the 10 deaths were from tuberculosis; in unvaccinated, the number was about 7 of the 20. These seem like good numbers (a 71% reduction in deaths from TB), though it's odd that all-cause mortality was so much different between the groups also. Seems like perhaps the two groups were not equivalent, but there aren't enough details to tell for sure.

The second question is whether the vaccine is safe, especially since it is a live organism (though attenuated). Some people had criticized it previously, but this article claims that they had mostly changed their minds, and all agreed it was safe. They don't show data, though, so who can say.

Overall they seem optimistic, but still have questions about how reliable and long-lasting the immunity is. Further studies are required.

Citation: Canadian Experience with BCG Vaccine. Can Med Assoc J 35, 196–197 (1936).