No one's quite sure how prevalent these symptomless, or asymptomatic cases are.

没有人能够确定这些无症状病例的情况究竟有多普遍。

But to break the chain, it behoves even the symptomless to assume that they might be infected.

但是为了打破这个链条，即使没有任何症状的人也应该假设他们可能被感染了。