Herd immunity can protect a population when the proportion of immune people exceeds the threshold 1 - 1/R0. For a disease with R0 = 5, what proportion must be immune?
Answer and explanation
Correct answer: D. More than 80 percent of the population
- Step 1: Threshold = 1 - 1/5 = 1 - 0.2.
- Step 2: = 0.80, so more than 80 percent need to be immune.
Answer
more than 80 percent.
Why not the others: 20 percent is 1/R0, not the threshold; 50 percent is a threshold for R0 = 2; 95 percent would suit R0 = 20.
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