Herd immunity threshold (HIT) is determined by the formula HIT = 1 − (1/R₀). For measles with R₀ = 15, the herd immunity threshold is approximately:
- A 85%
- B 93% ✓
- C 90%
- D 97%
Correct answer: B. 93%
Explanation
HIT = 1 − (1/R₀) = 1 − (1/15) = 1 − 0.067 = 0.933, approximately 93%. Measles has one of the highest R₀ values (12-18), requiring very high vaccination coverage (>95%) to achieve herd protection. This explains why even small drops in measles vaccination coverage lead to outbreaks. The MMR vaccine requires 2 doses to achieve >97% seroconversion.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.