There is no virus definition database that needs to be updated regularly, no subscription, and no service agreement.

没有病毒定义数据库，需要定期更新，没有订阅，没有服务协议。

youdao

In the latter case we don't have an opportunity to build up any immunity beforehand because it's, by definition, a new virus.

在近期的病例中我们没有机会提前建立任何免疫系统，因为从理论上来讲它是一种新的病毒。

youdao

New diseases are, by definition, poorly understood when they emerge, and this is most especially true when the causative agent is an influenza virus.

从定义上讲，人们对新出现的疾病了解很少，从病原体是流感这一点上可以看到这一点。

youdao

Each is equipped with a high definition photographic memory of the virus it helped destroy and it is primed and ready to prevent subsequent infection - but only if it encounters the same virus.

BBC: Winter bugs: A yearly battle for dominance