Tuberculosis

Frequently Asked Questions (FAQ)

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BCG is a live vaccine against tuberculosis (TB). BCG stands for Bacillus Calmette-Guerin after two doctors who introduced the vaccine. It was developed in the 1920's and remains the only vaccination available against TB today.

BCG can prevent someone getting TB about half the time although estimates vary widely. The protection BCG provides becomes less with time since vaccination. This means that many people develop active TB even though they received BCG.
Although BCG has been used widely for a long time the rates of TB in countries that use BCG have not changed. One third of the world's population has TB infection and two million people a year die of TB. BCG alone is not enough to stop the spread of TB.

BCG is very effective in the prevention of serious forms of TB, like TB meningitis or miliary TB, which can often lead to death. This is especially important for children because they develop severe TB much more often than adults. In areas of the world with high rates of TB the risk of children developing severe TB is high enough to make the use of BCG worthwhile.

In countries with high rates of TB, BCG is given to infants to help prevent the more serious forms of TB disease. In some countries BCG is given several times during childhood and early adult life, in an effort to maintain some protection against TB.

If effective, BCG will give a positive skin test. However, as time goes by, not everyone who had BCG will continue to have a positive skin test. If you have a positive skin test and are from a part of the world where TB is common, you should assume that it is due to TB exposure. BCG should not stop you from having a skin test.

BCG is not used routinely for a number of reasons. TB is not widespread so the chances are small that infants and young children will become exposed. There can be serious side effects in those with serious immune system problems. The exception to this is First Nations or Inuit infants, who live in communities with high rates of TB. Lastly BCG makes the TB skin test difficult to understand since one cannot be sure if a positive result is due to infection with TB or vaccination with BCG.

For people who require repeated skin testing, a 2-step test is done to establish a true baseline result. People who have been infected with TB in the past or had BCG years ago may have an initial negative result. However, a second test, given one or two weeks later, will be positive. This second test is accurate.