From the Guidelines
BCG live or attenuated vaccine is a live attenuated vaccine, and the most recent and highest quality study 1 suggests that it is effective in preventing TB meningitis and disseminated TB in children, but has highly variable efficacy in preventing other forms of TB, especially in adults.
Key Points
- BCG vaccine contains weakened but live Mycobacterium bovis bacteria that stimulate immunity without causing disease.
- The vaccine is most effective at preventing severe forms of TB in children, particularly TB meningitis and miliary TB, with efficacy ranging from 60-80% for these presentations, as noted in 2.
- However, its effectiveness against pulmonary TB in adults varies widely (0-80%) depending on geographic location, as mentioned in 3.
- The vaccine is contraindicated in immunocompromised individuals, including those with HIV, as the live bacteria can cause disseminated infection, as stated in 3.
- Side effects typically include local reactions at the injection site, such as redness, swelling, and formation of a small ulcer that usually heals within 2-3 months, leaving a small scar.
Recommendations
- BCG vaccination should be considered for infants and children who reside in settings in which the likelihood of M. tuberculosis transmission and subsequent infection is high, provided no other measures can be implemented, as recommended in 3.
- BCG vaccination may be considered for health-care workers who are employed in settings in which the likelihood of transmission and subsequent infection with M. tuberculosis strains resistant to isoniazid and rifampin is high, provided comprehensive TB infection-control precautions have been implemented in the workplace and have not been successful, as suggested in 3.
- The development of new, more effective vaccines and vaccination strategies is ongoing, with several new vaccine candidates being evaluated in clinical trials, as mentioned in 1.
From the Research
BCG Live or Attenuated Vaccine
- The BCG vaccine is a live attenuated vaccine, primarily used to prevent tuberculosis (TB) caused by Mycobacterium tuberculosis (M. tb) 4, 5, 6.
- It has been used for over 100 years and is mainly administered to newborns in countries with high TB prevalence 5.
- The vaccine works by inducing an immune response polarization towards a Th1 profile, which is effective against M. tb and other intracellular pathogens 4.
- BCG has also been shown to provide protection against other diseases, including respiratory viruses, and has been used as a vector to express recombinant proteins 4, 5.
Mechanism of Action
- The BCG vaccine induces a cellular immune response, characterized by the activation of CD4+ and CD8+ T cells, and the secretion of cytokines such as IL-2 and IFN-γ 4.
- It also elicits a humoral immune response, although this is generally modest 4.
- The vaccine has been shown to provide trained immunity, a type of innate immune response that can provide protection against unrelated pathogens 5.
Safety and Reactogenicity
- The BCG vaccine has a good safety profile, with common side effects including injection site erythema, induration, and ulceration 7.
- Reactogenicity is similar to that of primary BCG vaccination, and is not affected by pretreatment with isoniazid (INH) 7.
- The vaccine is susceptible to major anti-tuberculosis drugs, including INH, rifampicin, and ethambutol, making it treatable in cases of severe adverse events 8.