During a dengue outbreak investigation, a seroepidemiological survey finds that the proportion of immune individuals in the community is 70%. The basic reproduction number (R0) of dengue in this area is estimated at 4. The additional proportion of the population that still needs to become immune to reach the Herd Immunity Threshold is:
- A 0% — herd immunity threshold already exceeded
- B 5% ✓
- C 25%
- D 30%
Correct answer: B. 5%
Explanation
HIT = 1 – (1/R0) = 1 – (1/4) = 75%. Current immunity in population = 70%. Gap = 75% – 70% = 5%. An additional 5% must acquire immunity (through vaccination or natural infection) to reach the HIT. Since 70% < 75%, the threshold has not yet been reached; 25% represents the 1/R0 fraction and 30% represents the current susceptible proportion.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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