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GCSE Biology · key term
A person who is not immune to a pathogen and can therefore become infected.
Used by Edexcel
Specification 5.15B · Paper 1
Revise: Benefits and Risks of ImmunisationAn infected person can transmit a pathogen only if it reaches another susceptible host. When few people are immune, the pathogen can pass through a long sequence of susceptible people and an outbreak can grow. When many people are immune, an infected person is more likely to encounter people who do not support further transmission.
For an ‘explain herd immunity’ question, give the full causal chain: many people are immune → fewer susceptible hosts → fewer successful transmissions → chains of infection are more likely to break → unvaccinated people are less likely to encounter the pathogen.
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