Herd immunity occurs when

  1. everyone has had the disease
  2. pathogens mutate
  3. antibodies are given to all
  4. enough people are vaccinated that the pathogen cannot spread
Answer

D) enough people are vaccinated that the pathogen cannot spread

Few susceptible hosts remain. AS & A Level Biology · Topic 11 Immunity · 11.2 Antibodies and vaccination

Biology MCQ · More A Level Biology: Immunity MCQs · Practise