How does herd immunity help protect people who cannot be vaccinated?
Quick Answer
Herd immunity happens when enough people in a community are immune that a disease spreads less easily. This lowers the chance that vulnerable people will be exposed.
The Full Story
When a large share of a population is immune through vaccination or prior infection, transmission chains break more often. That protection helps shield infants, people with weakened immune systems, and others who cannot safely receive certain vaccines. The exact threshold depends on the disease: measles requires very high coverage because it is highly contagious, while less transmissible infections need a lower level. Herd immunity is not a fixed number and can be weakened by outbreaks, travel, or falling vaccination rates. Public health campaigns use coverage targets to keep diseases under control.
Key Facts
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