Okay, let's tackle this question about the Vi polysaccharide vaccine. First, I need to recall what the Vi polysaccharide vaccine is used for. I think it's for typhoid fever, caused by Salmonella typhi. The Vi antigen is part of the bacterial cell wall. Now, the question is asking which statement about this vaccine is true. But the options aren't provided, so I need to figure out possible options based on common facts.

The core concept here is understanding the characteristics of the Vi polysaccharide vaccine. The key points are its antigen type, target population, efficacy, and administration route. The Vi vaccine is a polysaccharide vaccine, not conjugated, which means it's less effective in children under two because polysaccharide vaccines don't elicit a strong immune response in young children. Conjugate vaccines, like the Typhoid Conjugate Vaccine (TCV), are better for that age group. Also, the Vi vaccine is administered subcutaneously or intramuscularly and provides protection for about 3-5 years. It doesn't contain live bacteria, so it's safe for immunocompromised individuals.

Now, considering common distractors, options might include things like being a live vaccine (wrong), giving lifelong immunity (incorrect), or being suitable for children under two (also incorrect). The correct answer would highlight that it's a polysaccharide vaccine with a specific administration route and age limitations.

For the explanation, I need to structure each section as per the user's instructions. The core concept is the nature of the Vi vaccine as a polysaccharide-based, non-conjugated vaccine. The correct answer's reasoning would involve its antigen type, administration method, and target age group. Each wrong option would be incorrect because they either misstate the vaccine type, administration route, or age suitability. The clinical pearl should emphasize the difference between Vi and conjugate vaccines, especially regarding age appropriateness and immune response.

I need to make sure the explanation is concise, fits within the character limit, and uses the correct medical terminology. Also, avoid any markdown except for the required bold sections. Let me check if I covered all the required sections and followed the formatting rules.

**Core Concept**
The Vi polysaccharide vaccine targets *Salmonella typhi* by immunizing against the Vi capsular antigen. It is a **non-conjugated polysaccharide vaccine**, which limits its efficacy in children under 2 years due to underdeveloped T-cell-dependent immune responses.

**Why the Correct Answer is Right**
The Vi vaccine is administered **subcutaneously or intramuscularly** and provides 3–5 years of protection. It does not contain live bacteria, making it safe for immunocompromised individuals. Its mechanism relies on inducing opsonophagocytosis by antibodies against the Vi antigen, reducing bacterial load. However, it lacks memory B-cell activation typical of conjugate vaccines, limiting durability.

**Why Each Wrong Option is Incorrect**
**Option A:** *“It is a live attenuated vaccine”* is incorrect. The Vi vaccine contains purified polysaccharides, not live bacteria.
**Option B:** *“It is recommended for children under 2 years”* is incorrect. Polysaccharide vaccines like Vi are ineffective in this age group; conjugate vaccines

✓ Correct Answer: D. Can be administered with yell ow fever and hepatitis A vaccine