The passage explains that herd immunity occurs when a large percentage of the population is vaccinated, which helps protect those who cannot receive vaccines. Option B correctly states this benefit. The passage does not suggest that herd immunity eliminates all diseases or replaces hygiene practices. It also does not mention reducing side effects. On the NEX exam, cause-and-effect questions require identifying the specific outcome discussed rather than making broad assumptions. Herd immunity’s protective effect on vulnerable individuals is the key idea.

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