If the antibodies don't stop the virus, the vaccine strain is changed.

如果抗体不能阻止病毒传播，就会改变疫苗株。

The traditional way to select a strain for the vaccine involves injecting ferrets with an influenza virus used to make a vaccine strain, harvesting the antibodies, and then mixing them with a virus isolated from a human who recently had influenza.

选择疫苗株的传统方法包括给雪貂注射用于制造疫苗株的流感病毒，收集抗体， 然后将它们与从最近感染流感的人身上分离出的病毒混合。