Bacille Calmette-Guérin (BCG) is a widely administered global vaccine, derived from a weakened form of Mycobacterium bovis. This vaccine holds significant importance in public health, playing a role in preventing certain diseases. Its long history and widespread use underscore its impact on health initiatives worldwide.
Understanding Bacille Calmette-Guérin
BCG is a live, attenuated bacterial vaccine, meaning it contains a weakened form of the bacteria that can stimulate an immune response without causing active disease. The vaccine’s development began in 1904 by French scientists Albert Calmette and Camille Guérin, who isolated Mycobacterium bovis from an infected cow. They meticulously cultivated this bacterium over 13 years, involving 230 passages on a bile-potato medium, to progressively reduce its virulence. This prolonged attenuation process resulted in a strain that could safely induce immunity.
Primary Application: Tuberculosis Vaccination
BCG’s most widespread application is as a vaccine against tuberculosis (TB), a bacterial infection primarily affecting the lungs. It is typically administered intradermally, meaning into the top layer of the skin. The vaccine is particularly effective in preventing severe forms of TB in children, such as miliary TB and TB meningitis. Studies show it can reduce the risk of severe tuberculosis in children by approximately 70% to 80%.
Despite its effectiveness in children, BCG’s efficacy against pulmonary TB in adults shows considerable variability, with reported protection rates ranging from 0% to 80%. This variability is a subject of ongoing research and is influenced by factors such as geographic location and specific BCG strains used. Globally, 157 countries had universal BCG vaccination programs for infants, reflecting its continued role in public health strategies, especially in regions with a high incidence of TB.
Beyond TB: Other Medical Uses
Beyond its primary use in TB prevention, BCG has a role in the treatment of non-muscle-invasive bladder cancer (NMIBC). As an immunotherapy, it is directly instilled into the bladder after tumor removal surgery. This direct application stimulates a localized immune response against the cancer cells to prevent recurrence or progression. While the exact mechanism is not fully understood, it is believed to encourage the growth and activity of immune cells within the bladder lining to target cancer cells.
BCG treatment for NMIBC involves an initial course of weekly instillations for six weeks, followed by maintenance therapy for one to three years. Clinical trials are also exploring other potential uses for BCG, including its effects on conditions like fibromyalgia and diabetes, where it might influence immune-signaling molecules. These investigational uses highlight the broader immunomodulatory properties of BCG beyond its anti-tuberculosis effects.
Exploring Different BCG Strains
During its development and cultivation, the original BCG strain underwent genetic modifications, leading to distinct “strains”. These strains, such as Danish 1331, Pasteur 1173P2, Tokyo 172-1, Glaxo 1077, Connaught, and Russian BCG-I, differ in their genetic makeup, growth characteristics, and antigen expression.
These genetic variations contribute to observed differences in their efficacy and side effect profiles, both for TB vaccination and bladder cancer treatment. For example, the protective efficacy against TB can vary significantly among strains, with some studies suggesting more virulent strains might offer better protection. Differences in how these strains activate the immune system can lead to variable outcomes in clinical settings, highlighting the complexity of BCG’s biological effects.