Herd immunity threshold (HIT) for a disease with basic reproduction number (R₀) of 5 is:
- A 60%
- B 75%
- C 80% ✓
- D 90%
Correct answer: C. 80%
Explanation
Herd immunity threshold = 1 − (1/R₀) = 1 − (1/5) = 1 − 0.2 = 0.8 = 80%. This is the proportion of the population that must be immune (through vaccination or prior infection) to interrupt sustained transmission. For measles (R₀ ≈ 12–18), HIT is 92–95%. For COVID-19 wild-type (R₀ ≈ 2–3), HIT was approximately 50–67%.
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.