BCG Vaccine
What is the BCG vaccine?
The Bacillus Calmette-Guerin (BCG) vaccine is given by injection to protect against tuberculosis. The vaccine contains a weakened (“attenuated”) form of a bacteria related to the one that causes tuberculosis. This stimulates the immune system to protect against tuberculosis. BCG has contributed to the dramatic decline in TB over the past 40 years. BCG vaccination is usually given to newborn babies, but can also be given to older children and adults who are considered to be at risk of developing TB, where potential contact with the disease could occur or has occurred.
How effective is BCG vaccine?
Studies have shown that BCG vaccine gives substantial protection in both school children and newborn infants. Furthermore, protection from BCG is greatest against the more serious forms of the disease such as TB meningitis in children.
How do you know a BCG vaccine has been successful?
A response is shown by the development of a characteristic flat scar at the injection site. This is taken to be a sign of a ‘successful’ BCG vaccination. However, sometimes the vaccine does not leave a scar even though the vaccine has ‘taken’ and will provide protection.
What further tests are needed?
If a scar is not present, and there is no documented evidence of BCG vaccine, a Mantoux test is offered. The Mantoux test involves injecting a small amount of a protein (“tuberculin protein”) into the skin with a needle and syringe. The test site is then examined about 48 hours later. The test is positive if a small red lump develops at the needle site. This reaction is similar to a “hive” or an insect bite and resolves without leaving any permanent mark. The size of the reaction may vary.
When is the Mantoux test used?
The Mantoux test may be used, for the investigation and diagnosis of TB or, as in this case, to test a person’s immunity to TB before giving them the BCG vaccine. The Mantoux test is usually done routinely before BCG vaccine is given (except in children aged between 3 months and six years old who are not in an at risk environment1) to decide if the vaccine should be given.
What is TB?
Tuberculosis, or ‘TB’, is caused by a bacterium (a "germ" called the tubercle bacillus or Mycobacterium tuberculosis). TB usually affects the lungs, but can affect other parts of the body, such as the lymph nodes (glands), bones, joints and kidneys and it can rarely cause meningitis. It is most commonly spread by the respiratory route: when a person with infectious TB of the lungs coughs or sneezes they produce infectious droplets which can be breathed in by another person. However, TB is generally spread only after quite close and prolonged contact with an infectious person such as a person living in the same household or with a similar degree of contact.
How common is TB?
In 1952, there were nearly 7,000 cases of TB notified in Ireland. The combination of better living conditions, antibiotics against TB, and BCG vaccine have dramatically reduced the number of cases of TB in Ireland. In 2008, the total number of cases notified nationally was 470. Detailed reports on the epidemiology of TB can be found here.
The people most likely to catch TB are the very young, the elderly and those with an immune system weakened either by illness or by certain medications.
More information on BCG vaccination is available in the BCG and vaccination sections of the HPSC website.
1. Children in at-risk environments include those who are contacts of a pulmonary TB case, who are from an area of high TB endemnicity (≥ 40 TB cases per 100,000 population per year) or whose parents are from an area of high TB endemnicity.
Last updated: 24 August 2010