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: Concept Summary:
Vaccines are categorized by their antigen type. This question concerns the classification of the typhoid vaccine based on the Vi antigen.
Step 2: Detailed Vaccine Type Analysis:
Analyzing vaccine types, focusing on the typhoid Vi vaccine:


Live attenuated vaccines: Employ a weakened pathogen (e.g., oral typhoid Ty21a vaccine).

Killed (inactivated) vaccines: Utilize a whole, inactivated pathogen (e.g., older whole-cell typhoid vaccines).

Subunit vaccines: Employ specific pathogen components (subunits) like proteins, sugars, or capsids, enhancing safety.

The typhoid Vi vaccine utilizes purified Vi capsular polysaccharide from Salmonella Typhi.

As this vaccine uses a specific bacterial component (polysaccharide capsule) instead of the whole organism, it is a subunit vaccine. It is specifically a polysaccharide subunit vaccine. A conjugate version exists with the polysaccharide linked to a protein carrier to enhance the immune response.

Step 3: Conclusion:
The typhoid Vi antigen vaccine is classified as a subunit vaccine.