Which disease is prevented by TAB vaccine?

A combination vaccine is formulated to immunise a person against several distinct pathogens, or against distinct serotypes of one bacterial species, through a single preparation. Typhoid and paratyphoid A and B are three such related but distinct infections — each caused by a different serotype of the bacterium Salmonella enterica (S. Typhi, S. Paratyphi A, and S. Paratyphi B respectively).

The TAB vaccine ("Typhoid–paratyphoid A and B" vaccine) is exactly this kind of combination preparation: it carries inactivated whole-cell antigens of S. Typhi together with S. Paratyphi A and B, so a single dose immunises a person against typhoid and paratyphoid fevers together.

The other three options given here are each prevented by an entirely different vaccine:

• Tuberculosis is prevented by the BCG (Bacillus Calmette–Guérin) vaccine — a live attenuated bacterial vaccine targeting Mycobacterium tuberculosis, an unrelated pathogen.

• Diphtheria is prevented by the diphtheria-toxoid component of the DPT/DTaP combination vaccine, which targets the toxin produced by Corynebacterium diphtheriae.

• Pertussis (whooping cough) is prevented by the pertussis component of that same DPT/DTaP vaccine, targeting Bordetella pertussis.

Since tuberculosis, diphtheria, and pertussis are each covered by a different vaccine altogether, the disease the TAB vaccine itself prevents, among the options given, is typhoid.