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Medicine

Epidemiological Modeling of Vaccine Hesitancy on Herd Immunity Thresholds

Quick fact

When vaccine hesitancy reduces uptake, the herd immunity threshold effectively rises, because some vaccinated individuals remain susceptible (due to incomplete efficacy) and unvaccinated individuals keep transmission alive. For measles, a drop in coverage from 95% to 90% can shift the threshold from R0-based calculations to a level where outbreaks become likely.

Why this is interesting

You’ve probably heard that vaccines protect the herd—but what happens when enough people refuse them? Could a small group of hesitant individuals unravel the entire shield?