What is BCG (Bacillus Calmette-Guerin) vaccine?

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BCG (Bacillus Calmette-Guerin) Vaccine

BCG vaccine is a live attenuated vaccine derived from Mycobacterium bovis that is primarily used for prevention of severe forms of tuberculosis in children, with limited application in the United States due to its variable efficacy in adults and interference with tuberculin skin testing. 1

Definition and Origin

BCG (Bacillus Calmette-Guerin) is a live vaccine derived from an attenuated strain of Mycobacterium bovis that was developed by Calmette and Guerin at the Pasteur Institute in France. It was first administered to humans in 1921 and has since become one of the most widely used vaccines globally, with more than 3 billion doses administered in 172 countries worldwide. 1, 2

Vaccine Characteristics

  • Types: Multiple BCG vaccine strains exist worldwide, all derived from the original M. bovis strain but with genetic variations due to different production techniques and passage over time 1, 3
  • Administration: Available for intradermal or percutaneous administration, depending on the specific formulation 1
  • Current US availability: The Tice strain is currently available in the United States, with Connaught Laboratories' strain under consideration for licensure 1

Efficacy

The protective efficacy of BCG vaccination varies significantly:

  • High efficacy (80-100%) for preventing serious forms of TB in children, particularly tuberculous meningitis and miliary TB 1, 2
  • Variable and equivocal efficacy (0-80%) for preventing pulmonary TB in adolescents and adults 1, 2
  • Geographic variation: Effectiveness appears higher in countries with high annual risk of TB infection 2

This variability in efficacy has been attributed to:

  • Different BCG strains used in various studies
  • Methods and routes of vaccine administration
  • Environmental factors and population characteristics
  • Exposure to non-tuberculous mycobacteria 3, 4

Indications for Use

In the United States, BCG vaccination is rarely indicated and not recommended for routine use. The primary strategies for TB control in the US focus on:

  1. Early detection and treatment of active TB cases
  2. Identification and preventive therapy for persons with latent TB infection
  3. Prevention of institutional transmission 1

BCG vaccination is reserved for specific situations:

  • Children: Should be considered for uninfected children who:

    • Have continuous exposure to persons with active TB and cannot receive isoniazid preventive therapy
    • Have continuous exposure to patients with TB strains resistant to both isoniazid and rifampin
    • Belong to groups with exceptionally high annual rates of new infection (>1% per year) 1

  • Healthcare Workers: May be considered only in settings where:

    • A high percentage of TB patients have multidrug-resistant TB (resistant to isoniazid and rifampin)
    • Transmission of such strains to healthcare workers is likely
    • Comprehensive TB infection control precautions have been implemented but have not been successful 1

Contraindications

BCG vaccination is contraindicated in:

  • Persons with HIV infection or other immunocompromising conditions
  • Persons on immunosuppressive therapy (corticosteroids, alkylating drugs, antimetabolites, radiation)
  • Pregnant women (unless at immediate excessive risk of TB exposure) 1

Adverse Effects

Common adverse effects include:

  • Local reactions (ulceration, muscular soreness, erythema) in 1-10% of vaccinees
  • Regional lymphadenitis
  • Rare but serious complications:
    • Disseminated BCG infection (0.06-1.56 cases per million doses)
    • BCG osteitis (0.01-43.4 cases per million doses, varying by country)
    • Higher risk of complications in immunocompromised individuals 1

Impact on Tuberculin Skin Testing

A significant limitation of BCG vaccination is its impact on tuberculin skin testing:

  • BCG vaccination can cause tuberculin reactivity ranging from no induration to 19mm
  • This reactivity typically wanes over time and is unlikely to persist >10 years after vaccination
  • The size of post-vaccination tuberculin reaction does not predict protection against TB
  • In BCG-vaccinated individuals, tuberculin skin test reactions ≥10mm should generally be attributed to TB infection rather than vaccination, especially in high-risk individuals 1

Global Perspective

While BCG use is limited in the United States, it remains an important component of TB control globally:

  • WHO recommends BCG vaccination for infants in TB-endemic countries
  • Approximately 130 million infants are vaccinated yearly worldwide
  • It is particularly valuable in developing countries with high TB prevalence for preventing severe forms of childhood TB 2, 5

Emerging Research

Recent research has explored potential non-TB-related benefits of BCG vaccination:

  • Possible protection against respiratory tract infections
  • Induction of "trained immunity" that may provide broader protection against other pathogens
  • Potential protective effects against COVID-19 (under investigation) 5

Despite being one of the oldest vaccines in use, BCG continues to be studied for improvements, with research focused on developing more effective, standardized TB vaccines with more durable protection and fewer side effects 6.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Research

[Update on the BGC vaccine. Indications for use in Europe and in developing countries].

Medecine tropicale : revue du Corps de sante colonial, 1996

6
Research

New vaccines for the prevention of tuberculosis.

Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 2002

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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