What is the BCG Vaccine?

BCG stands for Bacillus Calmette-Guerin, and is the name of a vaccine used to immunise against tuberculosis. This article looks at TB and its vaccination, and how BCG is currently used in the UK to immunise against the infection.

What is tuberculosis?

Tuberculosis is a bacterial infection often abbreviated to either MTB or TB. It is a very infectious illness that can often be fatal, and is made contagious by the fact that it can be spread through aerosolised droplets when a person suffering from an active TB infection coughs or sneezes.

TB is interesting in that most people suffer from a latent infection which presents with no symptoms. In these cases the person is infected with the bacteria, but is not contagious and won’t feel ill. 10% of latent infections will progress to an active form of the disease which, at present, is fatal about 50% of the time. Because of the high mortality associated with active infection, prevention is a priority and a lot of time and energy has gone into developing an effective vaccine against tuberculosis.

Active TB usually affects the lungs, and the symptoms associated with such an infection include a chronic cough producing a thick, often blood flecked, sputum. Sufferers also experience a fever and some weight loss, as well as bouts of night sweating.

The infection can spread to other organs, and in these cases symptoms can vary immensely. TB can be diagnosed through X-rays in which the infection is clearly visible, or through cultures where samples of fluid from the respiratory tract are sent to a laboratory for analysis.

Treatment is a major issue with TB because it takes months of regular antibiotic treatment to truly clear the body of infection. Unfortunately most people will find that their symptoms are resolved relatively quickly, and in many cases this leads to an interruption in the antibiotic regime which has given rise to strains of drug resistant tuberculosis. These strains of bacteria are extremely resistant to standard antibiotics and are becoming more common. Infections from drug resistant bacteria are referred to as multiple drug-resistant tuberculosis (MDR-TB).

As much as a third of the entire population of the world is thought to have been infected with TB, and the disease is spreading at a stunning rate of one new case per second. It is a major concern in developing countries, but can easily spread amongst communities here in the UK, particularly without adequate immunisation.

What is the BCG vaccine?

The BCG vaccine is an important step towards addressing the growing problem posed by tuberculosis and multiple drug resistant strains of TB.

BCG is a live, attenuated vaccine, meaning that it is made up of a weakened strain of the bacterium responsible for TB, Mycobacterium bovis. In this case the bacterium is weakened because it is a strain infectious amongst cows, and is therefore less effective amongst humans, giving our immune systems a chance to develop immunity against the disease long before the attenuated bacterium can cause an infection.

The evidence available to date suggests that BCG is 80% effective at preventing TB infections for 15 years. One of the issues with BCG thus far however, has been evidence that the effectiveness of the vaccine varies from place to place. 60-80% effectiveness is expected here in the UK, however studies in other parts of the world have shown huge variation in these figures, with some reporting efficacy as low as 14%. Moreover this variation seems to extend to different kinds of TB, so where the BCG vaccine is ineffective against pulmonary tuberculosis (affecting the lungs), it has proven effective against other variants like TB meningitis (affecting the protective coating around the brain) and military TB (whole body infiltration of TB infection).

How is BCG used in the UK?

Because effectiveness is known to be high here in the UK, the BCG vaccine is still extensively used. BCG immunisation was previously part of the childhood vaccination programme and given at the age of 13, however more recently the schedule has been changed and the vaccine is offered shortly after birth.  

Babies born in parts of London are offered the BCG vaccine because of an increased TB presence in those communities. BCG vaccines are also given to health care workers who are often in contact with TB carrying patients, and those who have recently been exposed to the infection.

Immunising against TB is a growing area of interest, and research is being conducted into newer and more effective ways of immunising against TB.

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