Question

What are the two primary components of a Typhoid Vi vaccine?

• A. Vi capsular polysaccharide and carrier protein
• B. Lipopolysaccharide and toxin
• C. Attenuated bacteria and adjuvant
• D. DNA plasmid and viral vector

Hint:

{Typhoid Vi Vaccine = Vi Polysaccharide + Carrier Protein}.
This conjugation enhances immune response and memory.

Answer 1

The Correct Option is A

Concept: Typhoid fever is caused by the bacterium {Salmonella enterica} serovar Typhi. One of the important virulence factors of this bacterium is the Vi (virulence) capsular polysaccharide antigen, which plays a key role in immune evasion. Vaccines targeting this antigen help the immune system recognize and combat the pathogen.
Step 1:Vi capsular polysaccharide antigen.
The Vi antigen is a polysaccharide capsule present on the surface of {Salmonella Typhi}. This antigen is used as the main immunogenic component of the Typhoid Vi vaccine.
Step 2:Need for a carrier protein.
Polysaccharides alone often produce weak immune responses, particularly in young children. To enhance immunogenicity, the Vi polysaccharide is conjugated to a carrier protein.
Step 3:Formation of the conjugate vaccine.
When the Vi capsular polysaccharide is linked to a carrier protein (such as tetanus toxoid), it stimulates a stronger and longer-lasting immune response. Thus, the two primary components of a Typhoid Vi vaccine are: [ \text{Vi capsular polysaccharide} + \text{carrier protein} ]