Bacille Calmette-Guerin (BCG) is a live, attenuated vaccine for tuberculosis (TB).

It was first used in 1921 and continues to be used in European and developing countries. It was discontinued in Canada as a routine vaccination in the early 1970’s.

The effectiveness of BCG is highly variable. BCG is most protective against meningeal and miliary TB in infants and children.

The protective effects of the vaccine decrease with time. BCG does not offer lifetime protection against TB infection or TB disease.

BCG vaccination is given to infants and young children in many European and most developing countries.

The BCG is essentially used in TB endemic countries as there is more risk of TB exposure in these countries. Its use has been discontinued in many industrialized countries because of low TB rates.

In Canada, the vaccine is currently given to selected groups of people who still have high rates of TB, e.g. newborns and infants living on First Nation reserves and in Inuit communities.

Yes. Tuberculosis skin testing is recommended and can be given to people who have received BCG vaccination in the past.

People vaccinated with BCG may have a positive TB skin test. However, this reaction is likely to have been caused by TB infection, as opposed to BCG, as the effects of BCG diminish over time.

Thus, adults with a positive skin test who were vaccinated as children should be considered to have TB infection.

Age when BCG administered History of BCG vaccination and relationship to
skin test results
0 to 1 years Only 1% have a positive skin test if tested > 10 years later.
Therefore, history of BCG in infancy can be ignored in all persons aged 10 years or older when interpreting an initial skin test reaction of 10 mm or greater.
1 to 5 years 10-15% will have a positive skin test up to 25 years later.
>= 6 years Up to 40% have persistent positive skin test later in life.

Prophylactic treatment should be considered for any BCG-vaccinated person with a positive TB skin test. You must rule out active TB prior to starting any patient on prophylaxis.

Prophylactic treatment should be considered for those at high risk of developing TB disease including:

  • Populations with a high prevalence of TB infection (e.g. immigrants from countries with a high TB incidence)
  • Close contacts of an active case
  • People from First Nations communities (particularly, more northern reserves) and Inuit communities with high rates of TB
  • Staff and residents of correctional facilities, shelters, long term care facilities and hospitals
  • People who are immunocompromised (e.g. those with renal failure, cancer, diabetes, or HIV/AIDS)
  • People with abnormal chest radiograph consistent with inactive TB

Public Health Agency of Canada and Canadian Lung Association/Canadian Thoracic Society. (2007). Canadian Tuberculosis Standards. (6th ed.). Ottawa