BCG is a vaccine for tuberculosis (TB). This vaccine is not widely used in the United States, but it is often given to infants and small children in other countries where TB is common. BCG vaccine does not always protect people from TB. Persons who were vaccinated with BCG may have a positive reaction to a TB skin test. This reaction may be due to the BCG vaccine itself or to a real TB infection.
But one’s positive reaction probably means that they have TB infection if:
- The BCG vaccination was administered many years ago (because the BCG reaction gets smaller over time)
- The person has ever spent time with a person with infectious TB
- The person is from a country where TB disease is very common (most countries in Latin America and the Caribbean, Africa, and Asia, except for Japan)
- The skin test reaction is large
- Someone in the person’s your family has had TB