Evaluation of safety and efficacy of new vaccines is likely to be especially challenging since the vaccines might not be available until after the pandemic had started.

由于这些新疫苗可能在流感大流行开始之后才能够获得，因而要评估它们的安全性和效力就很可能非常困难。

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Evaluation of safety and efficacy of new vaccines is likely to be especially challenging since the vaccines might not be available until after the pandemic had started.

由于这些新疫苗可能在流感大流行开始之后才能够获得，因而要评估它们的安全性和效力就很可能非常困难。

youdao