In a community of 200 000 people, 120 000 are vaccinated against measles. If the basic reproduction number (R0) of measles is 15, what percentage of the population needs to be immune to achieve herd immunity?

Step-by-step solution

1. Recall herd immunity threshold formula: $1-\frac{1}{R_0}$
2. Substitute $R_0=15$ to get $1-\frac{1}{15}=\frac{14}{15}$
3. Convert to percentage: $\frac{14}{15}\times 100\approx 93.33\%$
4. Round to nearest whole number: 93%

Concept tested: Herd immunity calculation

Published 19 September 2026 · How this solution was prepared and checked