True about typhoid vaccines are all except ?
**Core Concept**
Typhoid vaccines are used to prevent typhoid fever, a systemic infection caused by Salmonella Typhi. The primary mechanism of action involves inducing immunity against the bacteria, either through active or passive immunization.
**Why the Correct Answer is Right**
Vaccines against typhoid fever are classified into two main types: **inactivated (parenteral)** and **live attenuated (oral)**. The inactivated vaccines, such as the Vi polysaccharide vaccine, induce a humoral immune response, primarily through the production of antibodies against the Vi capsular antigen of S. Typhi. The live attenuated vaccines, such as Ty21a, stimulate both humoral and cellular immune responses, providing longer-lasting immunity.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we cannot evaluate its correctness.
**Option B:** This option is also not provided, so we cannot evaluate its correctness.
**Option C:** This option is not provided, so we cannot evaluate its correctness.
**Option D:** This option is also not provided, so we cannot evaluate its correctness.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the World Health Organization (WHO) recommends the use of the oral Ty21a vaccine for travelers to areas with high typhoid fever prevalence, while the Vi polysaccharide vaccine is recommended for individuals with a higher risk of exposure.
**Correct Answer:** Not provided