What is the Tuberculosis (TB) vaccine?

From the Guidelines

The TB vaccine, also known as Bacille Calmette-Guérin (BCG), is a vaccine primarily used to protect against tuberculosis, and its use is reserved for selected persons who meet specific criteria, such as infants and children who reside in settings with a high likelihood of M. tuberculosis transmission 1. The vaccine contains a weakened strain of Mycobacterium bovis, which stimulates the immune system without causing disease. BCG is typically administered as a single intradermal injection, usually in the upper arm, and is most commonly given to infants and young children in countries where TB is common. The vaccine is particularly effective at preventing severe forms of TB in children, such as TB meningitis and miliary TB, though its effectiveness against pulmonary TB in adults varies. In the United States and many other low-TB-incidence countries, BCG is not routinely recommended due to the low risk of infection and because it can interfere with tuberculin skin test results, making it harder to detect latent TB infection 1. Some key points to consider about the TB vaccine include:

• The vaccine is not recommended for children and adults who are infected with human immunodeficiency virus due to the potential adverse reactions associated with the use of the vaccine in these persons 1.
• BCG vaccination of health-care workers should be considered on an individual basis in settings where there is a high percentage of TB patients infected with M. tuberculosis strains resistant to both isoniazid and rifampin 1.
• The vaccine works by training the immune system to recognize and fight the bacteria that cause TB, providing some protection against future infection. Side effects are generally mild and may include a small sore at the injection site that can leave a small scar. It's worth noting that the recommendations for the use of BCG vaccine have been updated over time, and the current guidelines emphasize the importance of individualized decision-making and careful consideration of the risks and benefits of vaccination in different settings 1.

From the Research

Definition and Purpose of the TB Vaccine

• The TB vaccine, also known as the Bacillus Calmette-Guérin (BCG) vaccine, is a live attenuated M. bovis vaccine developed about 100 years ago by Albert Calmette and Camille Guérin 2.
• The primary purpose of the BCG vaccine is to protect against tuberculosis (TB), a bacterial infection that can cause serious health problems, particularly in children and individuals with weakened immune systems.

Mechanism of Action and Effects

• The BCG vaccine works by inducing an immune response that provides protection against Mycobacterium tuberculosis infection and TB disease 3.
• The vaccine has been shown to enhance IFN-γ and IL-10 levels, providing immunity against respiratory tract infections, even in elderly people 2.
• BCG vaccination also provides nonspecific innate immunity against viruses and parasites through a mechanism termed 'trained immunity' 2.

Efficacy and Effectiveness

• The efficacy of the BCG vaccine varies greatly between age groups and settings, with higher protection against TB in children than in adults 3.
• Studies have consistently shown that BCG vaccination is highly effective against childhood tuberculous meningitis and miliary tuberculosis, but its efficacy against adult pulmonary tuberculosis is variable 4.
• A recent meta-analysis found that BCG vaccination shows protective effectiveness against TB infection, particularly in low-TB incidence areas, with an overall protective effectiveness of 18% 5.

Administration and Recommendations

• The World Health Organization (WHO) recommends a single dose of BCG for infants in TB endemic and leprosy high-risk countries 2.
• Globally, almost 130 million infants are vaccinated yearly with the BCG vaccine 2.
• The vaccine is typically administered via intradermal injection, but research has also explored the use of oral and mucosal delivery routes to induce protective immune responses 6.