Single-dose measles vaccine limitations prevent elimination

Steps:

• Measles requires 95% population immunity for herd protection and elimination.
• Single-dose vaccine protects ~93% of recipients, leaving ~7% susceptible.
• Some children fail to develop full immunity after one dose, needing boosters.
• A one-dose program thus maintains transmission chains in unprotected groups.

Why B is correct:

• Measles vaccination protocols (e.g., WHO guidelines) mandate two doses because 5-10% of children do not achieve lasting immunity after one, requiring boosters for complete seroconversion.

Why the others are wrong:

• A: Passive immunity wanes by 6-9 months, but vaccination targets older children; it doesn't explain program failure.
• C: 95% efficacy highlights incomplete protection but doesn't address need for boosters in non-responders.
• D: Measles virus antigenic stability aids vaccine design but irrelevant to one-dose shortcomings.

Final answer: B