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You may have read that you can skip getting vaccinated if you live in a place 【小题1】 most people have had the disease or the vaccine (疫苗), allowing you to take advantage of herd immunity. “But effective herd immunity requires that more than 90 percent of the population be vaccinated 【小题2】 a disease”, says Tish Davidson medical writer and author of Vaccines: History, Science, and Issues and The Vaccine Debate. “The exact percentage depends on the contagiousness (接触传染性) of the disease, and the flu is very contagious. With the current low flu vaccination rate, people should not count on herd immunity 【小题3】 (protect) them.”