Explain how herd immunity helps to control the spread of measles in a population.
Answer
Herd immunity reduces measles transmission because a high proportion of immune individuals lowers the chance of an infected person encountering a susceptible host, thereby breaking the chain of infection.
Step-by-step solution
- State the definition of herd immunity: protection of susceptible individuals when a large fraction of the community is immune.
- Mention the basic reproduction number (R0) of measles is high (~12‑18), so a high immunity level (~95%) is needed.
- Explain that when most people are immune, an infected person is likely to meet immune hosts, reducing the number of new infections.
- Conclude that this interruption of transmission lowers overall incidence, protecting even those who are not immune.
Common mistake: Stating only that vaccination protects the individual, not the population effect
Concept tested: Herd immunity principle
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