What is bcg

What is the BCG Vaccine

The BCG vaccine, whose full name is Bacille Calmette-Guérin, is one of the oldest vaccines in the world still actively used today. Developed in 1921, it was created by French scientists Albert Calmette and Camille Guérin to protect against tuberculosis (TB), a serious infectious disease caused by the bacterium Mycobacterium tuberculosis. BCG is a live attenuated vaccine, meaning it contains a weakened form of the tuberculosis bacteria that trains the immune system to recognize and fight the disease without causing illness.

How BCG Works

BCG functions by stimulating the immune system to develop immunity against tuberculosis. When administered, the vaccine introduces a weakened form of the mycobacterium, which triggers the body's immune response. This prepares the immune system to recognize and combat the tuberculosis bacterium if the person is exposed to it in the future. The vaccine is particularly effective at preventing severe forms of tuberculosis in children, including meningeal TB and miliary TB, which can be fatal.

Administration and Schedule

BCG is typically administered as a single intradermal injection, meaning it is injected just beneath the skin's surface. The vaccine is usually given within the first few weeks of life, often as part of routine newborn immunizations. In some countries, BCG is administered at birth or within the first month, while in others it may be given later in infancy. The vaccine leaves a characteristic small scar at the injection site, which serves as evidence of vaccination.

Effectiveness and Protection

BCG provides approximately 70-80% protection against severe tuberculosis in children, with higher efficacy against childhood TB meningitis and disseminated disease. However, its protection against pulmonary TB (the most common form) in adults varies and may be lower. The duration of protection extends throughout childhood and adolescence, though immunity may wane over time. Because of variable effectiveness against TB in adults, BCG vaccination is just one component of comprehensive TB control strategies that also include testing and treatment.

Global Use and Importance

Over 180 countries include BCG in their national immunization programs, making it one of the most widely used vaccines in the world. The World Health Organization (WHO) recommends BCG vaccination for all infants in countries with a high tuberculosis burden. In countries with low TB incidence, such as the United States, BCG is generally not recommended for the general population but may be given to high-risk individuals. The vaccine remains crucial for global public health efforts to control and eliminate tuberculosis.