Question

In which of these conditions is post-exposure prophylaxis NOT useful?

• A. Measles
• B. Rabies
• C. Pertussis
• D. Hepatitis B

Hint:

Measles, rabies, and hepatitis B all have effective vaccine or immunoglobulin based PEP; pertussis instead relies on antibiotic chemoprophylaxis.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
Post-exposure prophylaxis (PEP) means giving a vaccine, immunoglobulin, or drug right after someone has been exposed to an infection, so as to stop or soften the disease before it sets in. We need the disease where this approach does not work.

Step 2: Key Concept:
PEP works best when the incubation period of the disease is long enough to let the body build protection, or when a ready-made antibody (immunoglobulin) can be given straight away.

Step 3: Detailed Explanation:
In measles, a contact can be given the measles vaccine within 72 hours of exposure, or immunoglobulin within 6 days, since measles has an incubation period of about 10 to 14 days, long enough for protection to build.
In rabies, PEP is the standard of care: wound care plus rabies vaccine and, where indicated, rabies immunoglobulin, since the incubation period is usually weeks to months.
In hepatitis B, a non-immune contact (for example a needle-stick exposure) is given hepatitis B immunoglobulin (HBIG) together with the vaccine, and this combination works well because the incubation period runs into weeks to months.
Pertussis (whooping cough) has a short incubation period of about 7 to 10 days, and there is no vaccine-based post-exposure prophylaxis that reliably prevents disease in an exposed contact. Instead, close contacts of a pertussis case are given a short course of a macrolide antibiotic (chemoprophylaxis), which is a different strategy from vaccine or immunoglobulin based PEP.

Step 4: Final Answer:
Because pertussis is not prevented by a vaccine or immunoglobulin given after exposure, option (C), Pertussis, is the correct answer.