ABSTRACT
Bacillus Calmette-Guérin (BCG) is a live vaccine and has the potential to cause local disease and systemic dissemination in immunocompromised hosts, including infants who are infected with human immunodeficiency virus (HIV) through vertical transmission, and patients with primary immunodeficiencies (PID) such as severe combined immunodeficiency (SCID), chronic granulomatous disease (CGD), hyper-IgM syndrome, and defects of the IL12- IFNγ axis (Mendelian susceptibility to mycobacterial diseases, MSMD). Disseminated BCG is extremely difficult to treat. The chance of complete eradication is low unless functional immune response is restored by haematopoietic stem cell transplant. Prolonged use of anti-mycobacterial drugs often causes organ toxicities and drug resistance. Inflammatory complications which develop upon immunoreconstitution post-transplant may necessitate immunosuppressive treatment, which adversely affect immune recovery and increases risks of opportunistic infections. Multiple BCG reactivations can occur in patients with CGD and MSMD, and BCG can remain latent until reactivations take place in adulthood and manifest as disease. It is important for neonatologists, general practitioners, primary care clinicians and nurses working in maternal and child care centers to be aware of BCG-related complications, which may be the first sign of an underlying immunodeficiency. As neonatal BCG is included in standard vaccination schedule in many countries, it is a challenge to identify and avoid administration of BCG to infants who potentially have PIDs. Deferring BCG vaccination is recently advocated to protect highly vulnerable populations, but the appropriate strategy is yet to be determined. Newborn screening for SCID offers a potential to avoid this complication, if an integrated system of screening and vaccination can be organised.
Tuberculosis (TB) is endemic in Asia. Out of 22 countries with high TB burden, 10 are Asian countries. Bacillus Calmette-Guérin (BCG) vaccine is one of the world’s most widely used vaccine. It is a live vaccine made from attenuated strains of Mycobacterium bovis (M. bovis). BCG vaccine has consistently shown high efficacy against childhood tuberculous meningitis and miliary TB, while efficacy against adult pulmonary TB and other mycobacterial diseases is more variable. In a study performed by Trunz et al, it was estimated that 100 million doses of BCG vaccine given to children every year prevent about 40,000 cases of TB meningitis and miliary TB before these children reach their fifth birthdays, or roughly 1 case prevented for every 2500 inoculations. In particular, the numbers of cases prevented would be highest in Southeast Asia (46%), compared with 27% in sub-Saharan Africa and 15% in the Western Pacific region. The coverage rate of BCG vaccine in Southeast Asia and Western Pacific is 88% and 97%, respectively.
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