即使在感染你的时候，感冒病毒也会发生变异，而且新的病毒毒株经常出现，以至于当制药商研制出针对其中一种变异的疫苗时，血清已经过时了。
Colds mutate even while they're infecting you, and new strains pop up so often that by the time drug-makers create a vaccine against one variation, the serum is already out of date.
该病毒是否会产生变异，成为毒性更强的病毒株，仍有等观察。
It remains to be seen whether the virus will mutate into a more virulent strain.
一般在同一时候都有好多种不同的流感病毒株在活跃，而且这些病毒株在不断变异。
There are usually several different strains of influenza active at any time, and these variations evolve.
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