英语语法分析

There are two crucial factors: the transmissibility of the virus, and its virulence.

有两个关键因素：病毒的传播性和其毒性。

The virus can improve its transmissibility among humans via two principal mechanisms.

病毒可通过两种主要机制加强其在人群中的传播能力。

The Science study also provided the first estimate of the person-to-person transmissibility of H1N1.

“科学”研究还提供了H1N1人对人传播的初期评价。