Which is a live attenuated vaccine?

AIIMS Delhi NO - 2017

Pharmacology

Easy

Appeared in: AIIMS Delhi NO - 2017

Explanation

BCG (Bacillus Calmette-Guérin) is a classic example of a live attenuated vaccine.
It is prepared from a live, weakened strain of Mycobacterium bovis, a bacterium that is closely related to Mycobacterium tuberculosis, the agent of human tuberculosis.
Live attenuated vaccines work by mimicking a natural infection, which stimulates a strong, long-lasting cell-mediated and humoral immune response.
Other examples of live attenuated vaccines include Measles, Mumps, Rubella (MMR), Oral Polio Vaccine (OPV), and Yellow Fever.

Option B: DPT is a combination vaccine, but none of its components are live attenuated. The Diphtheria and Tetanus parts are toxoids (inactivated toxins), and the Pertussis part is a whole-cell inactivated (killed) bacterium.
Option C: TT stands for Tetanus Toxoid. As the name implies, it is a toxoid vaccine, not a live vaccine. It contains the inactivated toxin produced by the tetanus bacteria, which stimulates the body to produce antitoxin antibodies.
Option D: The Hepatitis B vaccine is a recombinant subunit vaccine. It is created using genetic engineering to produce one of the virus's surface proteins (Hepatitis B surface antigen - HBsAg). It contains no live viral components.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of Vaccines as background academic context rather than a clinical decision trigger.
A crucial nursing responsibility is to know the type of vaccine being administered, as it has significant clinical implications. Live attenuated vaccines are generally contraindicated in immunocompromised individuals (e.g., patients with HIV/AIDS, undergoing chemotherapy, or on long-term steroid therapy) and pregnant women because the weakened pathogen could potentially cause disease in them.
Patient education is key. Nurses must explain the type of vaccine, its benefits, and potential side effects. For BCG, this includes explaining the expected local reaction (a small pustule that heals leaving a scar), which is a sign of successful vaccination.
What if? If the patient was a newborn whose mother has active, infectious tuberculosis, the standard recommendation is to give the infant isoniazid prophylaxis first, and delay the BCG vaccine until the prophylaxis is complete. This is because BCG's effectiveness is reduced in the presence of active TB exposure and treatment.

How to Approach the Question

First, identify the key term in the question stem: 'live attenuated vaccine'. This tells you the question is about vaccine classification.
Second, recall the definitions of different vaccine types: live attenuated, inactivated (killed), toxoid, and subunit/recombinant.
Third, systematically evaluate each option against the definition of a live attenuated vaccine.
Option A, BCG, is known to be a live vaccine for TB. Option B, DPT, is a mix of toxoids and killed bacteria. Option C, TT, is a toxoid. Option D, Hep-B, is a recombinant vaccine.
Based on this classification, conclude that BCG is the only live attenuated vaccine in the list.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart A (pp 26-201 of 604) pp. 96-98, 97-99