And not all vaccines offer long term protection. The tetanus vaccine is a good example. It offers protection for only about ten years. Then a person must be immunized again.

• 也不是所有的疫苗都是终身有效的，比如破伤风疫苗就是个很好的例子，它只能提供十年的收效保护期，过了十年，就必须要重新接种疫苗。