Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), plays a significant role in causing illness and mortality, especially in developing nations. The prevailing approaches to TB control in many developing countries prove insufficient due to the escalating prevalence of drug-resistant strains, the exorbitant cost of medications, and various socioeconomic challenges.
In the majority of individuals with a primary infection, clinical manifestations often go unnoticed, potentially advancing to cavitary pulmonary tuberculosis, extra-pulmonary tuberculosis, disseminated tuberculosis, or meningitis.
The sole vaccine presently accessible for tuberculosis prevention is BCG (Bacille Calmette-Guerin), formulated in 1921. The BCG vaccine has proven efficacy in safeguarding children against meningitis and disseminated tuberculosis. A recent analysis revealed that children who received the BCG vaccine and were exposed to individuals with open pulmonary TB (PTB) exhibited a 19% lower infection rate compared to unvaccinated children (95% CI: 8–29), indicating a level of protection against primary disease.
Nonetheless, there is no substantiated evidence supporting its efficacy in preventing the reactivation of latent pulmonary infection, which serves as the primary source of bacillary spread within the community. Consequently, the influence of BCG vaccination on the transmission of Mycobacterium tuberculosis is constrained. Nevertheless, BCG vaccination remains a crucial and life-saving element within standard tuberculosis control measures in the majority of endemic countries.
The protective effect of BCG against leprosy, as indicated by controlled trials, falls within the range of 26% to 41%. Despite this, BCG is not specifically employed for leprosy control. Additionally, BCG has demonstrated effectiveness in preventing Buruli ulcer caused by M. ulcerans.
A particular formulation of BCG is utilized in treating superficial forms of bladder cancer, eliciting a localized immune response against the tumor. In Sri Lanka, BCG vaccination enjoys a coverage rate of 99%.
Vaccine Type
BCG is categorized as a live attenuated vaccine, consisting of an M. bovis strain that has undergone multiple passages by Calmette and Guérin. Various strains of the BCG vaccine are accessible, all originating from a common source—namely, the Bacille Calmette-Guérin strain. In terms of efficacy, no BCG strain has been conclusively proven to be superior to another, and there exists no worldwide consensus regarding the optimal BCG strain for general use.
Effectiveness
BCG exhibits effectiveness within the range of 60-80% in non-endemic countries, but its efficacy is notably lower in endemic regions. Nevertheless, the average protection against TB meningitis and disseminated disease is marked at 86%. Consequently, childhood immunization with BCG has led to a significant decrease in the occurrence of miliary tuberculosis and tuberculous meningitis in children. For individuals vaccinated as neonates, the safeguarding against pulmonary tuberculosis (PTB) is measured at 59%.
Indications
In endemic countries like Sri Lanka, it is recommended to administer the BCG vaccine promptly at birth or as soon as feasible, preferably before discharge from the hospital, encompassing low birth weight and premature infants.
Vaccination for Older Age Groups
Consideration for BCG vaccination in older age groups is recommended under the following circumstances:
- Unvaccinated older children, adolescents, and adults residing in high-incidence areas of TB and/or leprosy.
- Unvaccinated older children, adolescents, and adults relocating from low-incidence to high-incidence TB and/or leprosy settings.
- Unvaccinated individuals or those testing negative for tuberculin skin test (TST) or interferon-gamma release assay (IGRA) at risk of occupational exposure in both low and high TB incidence areas. This includes professionals such as healthcare workers, laboratory staff, medical students, and prison workers.
Revaccination
- Research indicates minimal or negligible evidence supporting any added advantages of repeating BCG vaccination for protection against TB or leprosy. Consequently, revaccination is not advised, even in cases where the tuberculin skin test (TST) reaction or results of an interferon-gamma release assay (IGRA) are negative. It’s crucial to note that the absence of a BCG scar post-vaccination does not necessarily imply a lack of protection.
- Nevertheless, the National Immunization Programme (NIP) suggests that children aged between 6 months to 5 years, who do not exhibit a BCG scar following initial vaccination, should undergo revaccination without the need for a tuberculin skin test.
Contraindications
- Hypersensitivity to any component of the vaccine.
- Symptomatic or asymptomatic HIV disease – However, if individuals with HIV are initiated on anti-retroviral therapy (ART), are clinically stable, and show immunological stability (CD4 T lymphocyte percentage >25% in children under 5 years or CD4 T lymphocyte count ≥200 cells/µL if aged >5 years), consideration may be given to BCG administration, particularly for those residing in high-incidence TB settings.
- Congenital immune deficiency disorders.
- Malignant disease.
- Individuals undergoing immunosuppressive treatment.
Precautions
- Asymptomatic neonates born to mothers with TB should initially undergo preventive therapy with 6 months of prophylactic isoniazid, followed by BCG vaccination.
- In instances where infants have been exposed to smear-positive pulmonary TB shortly after birth, BCG vaccination should be postponed until the completion of 6 months of prophylactic isoniazid treatment.
- Neonates with a family history of immune deficiency disease should undergo investigation before vaccination. In the event of inadvertent vaccination, consultation with an infectious disease specialist is recommended, and anti-tuberculous therapy should be administered if clinically indicated.
- If there is a history of unexplained sibling death in infancy, the baby should be investigated for immunodeficiency before the administration of BCG.
Vaccination is not necessary to postpone in children with common illnesses like the common cold, asthma, or eczema, and in children taking antibiotics, provided they are not seriously ill.
A local reaction is a common occurrence after BCG vaccination. A few days post-vaccination, an induration develops at the injection site, gradually evolving into a small papule and eventually forming an ulcer within 2-4 weeks. Typically, the local reaction subsides in 2-5 months, resulting in a superficial scar. While the presence of a scar serves as an indicator of prior BCG vaccination, it does not necessarily signify protection against TB. It’s noteworthy that approximately 10% of vaccine recipients may not develop a scar.
Adverse Effects
In rare instances, an abscess may manifest at the site of injection. Axillary or, more rarely, cervical adenitis (referred to as BCGitis) may result in suppuration in exceptional cases. Severe injection site reactions are most commonly attributed to faulty injection techniques.
There is no unanimous agreement regarding the management of BCGitis. Generally, treatment is deemed unnecessary for local reactions, and there is no evident benefit derived from active interventions such as pharmacologic treatment, needle aspiration, or surgical excision.
Storage
Temperature: 2–8°C.