The Bacille Calmette-Guérin (BCG) vaccine is widely used globally and has played a significant role in public health for decades. Developed to address a widespread infectious disease, it remains a component of immunization programs worldwide.
Understanding the BCG Vaccine
The BCG vaccine is named after its French bacteriologist creators, Albert Calmette and Camille Guérin, who developed it between 1908 and 1921. It is a live-attenuated vaccine, meaning it contains a weakened form of a bacterium. Specifically, it is derived from Mycobacterium bovis, a bacterium closely related to Mycobacterium tuberculosis, which causes tuberculosis (TB).
The primary purpose of the BCG vaccine is to provide protection against tuberculosis, particularly the severe forms of the disease that affect infants and young children. It offers strong protection against life-threatening manifestations such as TB meningitis, which affects the brain, and disseminated TB, where the infection spreads throughout the body. While it significantly reduces the risk of severe disease in children, its effectiveness against pulmonary TB in adults can be variable.
How the Vaccine Works and is Administered
The BCG vaccine functions by stimulating the body’s immune system. When the weakened Mycobacterium bovis bacteria are introduced, they prompt the immune system to develop a defense mechanism against Mycobacterium tuberculosis. This prepares the body to fight off actual TB infection if exposed later.
The vaccine is administered as a single intradermal injection, typically into the topmost layer of skin on the upper arm, often over the left deltoid area. A short, narrow needle is used, inserted at a shallow angle. This method often results in a characteristic scar at the injection site, indicating a successful immune response. Target populations include infants and young children in areas with a high incidence of TB. In specific circumstances, healthcare workers or other high-risk individuals may also receive the vaccine.
Global Use and Why It Varies
Routine BCG vaccination is widely implemented in many countries where tuberculosis is prevalent. This includes regions with a high burden of TB, such as many parts of Asia, Africa, and Eastern Europe, where it is often given to infants shortly after birth as part of routine immunization programs. This widespread use has contributed to a reduction in TB-related mortality and morbidity.
In contrast, countries with a low incidence of TB, such as the United States, Canada, and many Western European nations, do not routinely administer the BCG vaccine. This variation is influenced by several factors. One reason is the lower risk of TB exposure in these settings. Additionally, BCG vaccination can interfere with the Mantoux tuberculin skin test, a common diagnostic tool for TB infection, by causing a false-positive reaction. In low-incidence areas, the focus shifts to identifying and treating active TB cases and latent infections through diagnostic testing, which can be complicated by prior BCG vaccination.
Post-Vaccination Expectations
After receiving the BCG vaccine, a predictable local reaction occurs at the injection site. Initially, a small, painless red bump may appear within two to four weeks. This bump then softens, potentially oozing pus, and eventually forms a crust.
The sore heals over several weeks or months, typically within two to four months, leaving a small, flat, permanent scar. This scar indicates a successful immune response. While this local reaction is expected, minor side effects can also occur, such as a mild fever, headache, or swollen glands in the armpit on the same side as the injection. If the injection site shows unusual or severe reactions, such as a large, persistent discharging abscess, or significant swelling and tenderness of the lymph nodes in the armpit, seek medical attention.