BCG Vaccine for TB: Benefits, Risks & Current Global Recommendations

Bacillus Calmette-Guérin (BCG) remains the only licensed tuberculosis vaccine. First used in 1921, it offers variable protection and is not routinely administered in low-incidence countries such as the United States.

Benefits

• Severe pediatric TB: 70–80% efficacy against TB meningitis and miliary TB in children
• Leprosy cross-protection: 20–50% efficacy
• Non-specific immune training: Trained immunity reduces all-cause mortality in infants (per RCTs)
• Bladder cancer therapy: Intravesical BCG is standard of care for non-muscle-invasive bladder cancer (NMIBC)

Risks & Side Effects

• Local (90%+): Papule → ulcer → scar (expected); suppurative lymphadenitis (1–10%)
• Systemic (rare): Fever, rash, osteitis, disseminated BCG disease (immunocompromised: 1–400 per million)
• Contraindicated: HIV (even asymptomatic), pregnancy, immunosuppression, acute illness
• False-positive TST: Complicates latent TB infection screening; IGRA preferred post-BCG

Efficacy Limitations

• Variable pulmonary TB protection (0–80%) — wanes over 10–20 years
• No impact on reactivation from latent TB infection
• Interferes with tuberculin skin test interpretation

WHO Recommendations (2023)

• Universal at birth: High TB burden countries (≥1% annual infection risk)
• Selective: High-risk groups in low-burden countries (healthcare workers, travelers to endemic areas, contacts)
• Not recommended: General population in low-incidence settings (US, Canada, Western Europe)

US Policy

• Not routinely administered
• Considered for: Children <5 with negative IGRA/TST who are continually exposed to infectious MDR/XDR-TB cases and cannot be separated
• Healthcare workers: Based on facility risk assessment

Future Vaccines

14 candidates are in clinical trials (subunit, viral vector, mRNA, whole-cell). M72/AS01E showed 50% efficacy in latently infected adults (Phase 2b). The goal aligns with WHO End TB Strategy targets.