VOA慢速英语:多少人接种疫苗才能形成群体免疫？

immune – adj. having special protection from something; of or relating to the body's immune system

refer – v. to talk or write about someone or something

precaution – n. something that is done to prevent possible harm or trouble from happening in the future

efficacy – n. the power to produce a desired result or effect

respiratory – adj. medical: of or relating to breathing or the organs of the body that are used in breathing

shed – v. to get rid of (something); to lose (leaves, skin, fur, etc.) naturally

suppress – v. to slow or stop the growth, development, or normal functioning of (something)