BCG (Bacillus Calmette–Guérin) Vaccine is used to prevent Tuberculosis (TB). BCG vaccine strains have evolved from the original Mycobacterium bovis isolates (from the infected cows) that vaccine inventors, Calmette and Guérin, cultured through numerous cycles during the 13-year period 1909–1921.
Repeated culturing of bacterial strains in a culture medium coaxes them to evolve and lose their virulence. In other words, bacteria become incapable of inducing the disease when injected into the human host. Still, structurally they are similar enough to their wild ancestors to awaken the immune response against human Tuberculosis. Such strains are called attenuated live vaccine strains. BCG vaccine has been used since 1921 and is undoubtedly one of the most widely used vaccines.
How is the BCG vaccine given?
BCG Vaccine is injected intradermally in the deltoid muscle of the arm. Vaccination is validated by the emergence of a scar due to ulceration at the site of insertion within a few months. Revaccination in absence of scar should be done in countries where TB is widespread.
BCG vaccine is given as a single dose, ideally at birth or at first contact of the baby with the outer world, but can also be given along with other routine vaccines at 6 weeks from birth. The catch up dose can be given till 5 years in the absence of vaccination at birth or if scar on the arm does not appear. Tuberculin testing prior to injection of the second dose of BCG is not necessary.
BCG vaccine should be given in the following cases:
- All newborns in India
- Workers in the health care who are exposed to patients having multidrug-resistant TB
BCG Vaccine should be avoided in the following cases:
- Older infants or children suspected of being HIV-infected or having leukemia, lymphoma or generalized malignant disease should not be vaccinated if they show symptoms of the disease or other evidence of immunosuppression
- Patients under treatment with immunosuppressants like corticosteroids, alkylating agents, antimetabolites and radiation
- Pregnant women
How effective is the BCG vaccine?
BCG vaccine is able to protect about 50% of recipients against Tuberculosis (TB) of the lungs. People who are vaccinated may also become sick with TB, but 80% of them are still protected from life threatening forms of disease such as Miliary disease and Meningitis. Vaccination in earlier childhood improves the chances of prevention.
The rationale to administer BCG vaccination immediately after birth or in early childhood is further strengthened with the recent study by the London School of Hygiene & Tropical Medicine (Dec 19, 2013) *. The study has proved the efficacy of BCG, the only licensed TB vaccine, in preventing the pulmonary TB found in lungs, if given to those who have no history of prior infection, including young infants. People who get the pulmonary TB disease, even after vaccination may be those who got infected with bacteria before the vaccine was given to them.
Side Effects of the BCG vaccine
TB vaccination can cause redness, swelling, soreness or ulceration at the injection site. Moderate swelling of the lymph nodes in the armpits or neck, which may give rise to pus-filled nodes that require drainage, can occur in very few cases. These reactions occur very rarely and may last up to three months. In extreme rare cases, the live attenuated TB vaccine can cause TB meningitis or disseminated TB.
New vaccines against TB
With advancements in mycobacterial genomics, there has been an increase in potential vaccine candidates. Scientists are able to investigate the immunological shortcomings of current BCG vaccine. The research aims at developing vaccines to prevent fresh infection, reactivation of latent infection and relapses in TB patients. Latest ongoing research plans include development of recombinant tailored BCG vaccines, attenuated strains of Mtb, subunit vaccines and DNA vaccines.
*Mangtani, I. Abubakar, C. Ariti, R. Beynon, L. Pimpin, P. E. M. Fine, L. C. Rodrigues, P. G. Smith, M. Lipman, P. F. Whiting, J. A. Sterne. Protection by BCG against tuberculosis: a systematic review of randomised controlled trials. Clinical Infectious Diseases, 2013; DOI: 10.1093/cid/cit790
Marketed BCG Products
Here is the list of WHO pre-qualified vaccine products available in market. Click on name of the product to know more.