Question

Typhoid Vi antigen type of vaccine is:

• A. Bacterial products
• B. Killed products
• C. Live products
• D. Subunit

Hint:

If a vaccine is named after a specific part of a pathogen (like the "Vi antigen" or "Spike protein"), it is almost always a \textbf{subunit} or \textbf{recombinant} vaccine. These vaccines isolate a key antigenic component to induce a targeted immune response.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Vaccines are classified based on the nature of the antigen they contain. The question asks to classify the typhoid vaccine that is based on the Vi antigen.
Step 2: Detailed Explanation:
Let's analyze the types of vaccines and the typhoid Vi vaccine specifically:


Live attenuated vaccines use a weakened form of the germ (e.g., oral typhoid vaccine Ty21a).

Killed (inactivated) vaccines use the whole, killed germ (e.g., the older whole-cell typhoid vaccine).

Subunit vaccines use only specific pieces (subunits) of the germ, like its protein, sugar, or capsid. This makes them very safe as they cannot cause the disease.

The typhoid Vi vaccine is based on the purified Vi capsular polysaccharide from the bacterium Salmonella Typhi.

Since this vaccine uses only a specific component (the polysaccharide capsule) of the bacterium rather than the whole organism (live or killed), it is classified as a subunit vaccine. Specifically, it's a polysaccharide subunit vaccine. There is also a conjugate version where the polysaccharide is linked to a protein carrier to improve immunogenicity.

Step 3: Final Answer:
The typhoid Vi antigen vaccine is a type of subunit vaccine.