而且，随着大流行病在国内和国际上波浪式相继传播，病毒的内在毒力可能会逐渐发生变化。
In addition, the inherent virulence of the virus can change over time as the pandemic goes through subsequent waves of national and international spread.
每个季度都要制造新的流感疫苗是因为流感病毒会不断地变化从而逃避宿主(无论是人类、鸟类还是其他动物)免疫防线的攻击。
New flu vaccines need to be made each season because the viruses are constantly changing so as to avoid attack by host immune defences - whether in birds, humans or other animals.
当细胞或病毒被冷却时，它们的薄膜往往会突然变化——近似于水分子在结冰过程中的重组方式——这样会挣破薄膜杀死细胞。
When cells and viruses are cooled, their membranes often change suddenly - similar to the way water molecules reorganize during freezing - and this can rupture the membrane and kill the cell.
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