B.C.G. vaccine prevents from which disease?

The Bacille Calmette-Guerin (BCG) vaccine is a live attenuated vaccine prepared from a weakened strain of Mycobacterium bovis. It is given as part of India's Universal Immunization Programme, ideally at birth, to build early cell-mediated immunity against one specific mycobacterial disease.

BCG specifically targets Tuberculosis (T.B.), which is caused by the bacterium Mycobacterium tuberculosis. The vaccine primarily protects infants against severe childhood forms of the disease, such as TB meningitis and disseminated (miliary) TB.

Checking against the other options confirms that each disease listed is prevented by a different, unrelated vaccine:

• Small Pox is caused by the variola virus and was prevented by the smallpox (vaccinia) vaccine; the disease was declared globally eradicated in 1980.

• Diphtheria is caused by Corynebacterium diphtheriae and is prevented through the diphtheria toxoid included in the DPT/pentavalent vaccine, not BCG.

• Typhoid is caused by Salmonella typhi and is prevented by the typhoid conjugate vaccine (TCV), a vaccine unrelated to BCG.

Since BCG's target organism is Mycobacterium tuberculosis, the vaccine's protective role is against Tuberculosis.