She explains that health workers have been using what I are called trivalent vaccins vaccines in some places.These are areas like Afghanistan where more than one kind of polio virus exists.

• 她说在一些像阿富汗一样有多种脊髓灰质炎病毒存在的地方，医务工作者已经开始使用这些俗称的“三价疫苗”。