Evaluate the statements above with respect to measles or polio, as the parent poster points out. It is clear that measles and polio vaccines can lead to "herd i

Evaluate the statements above with respect to measles or polio, as the parent poster points out. It is clear that measles and polio vaccines can lead to "herd immunity", while preventing severe side effects of these diseases in the majority of cases. The point is there is a range of infection mechanisms for viruses (respiratory vs other, for starters) and vaccines thus provide benefit at different points in the infection process. This leads to heterogeneity in "infection level" and symptomaticity in the vaccinated population.