种了一次牛痘，起预防作用。

Vaccination has a preventive effect.

接种牛痘能使人免患天花。

Vaccination immunizes one against smallpox.

所有儿童都种了牛痘以预防天花。

The children were all vaccinated against smallpox.

一位英国医生爱德华•琴纳(EdwardJenner)，发现通过接种感染牛痘脓疱可以预防天花。

An English physician, Edward Jenner, discovered that by inoculating a person with pustules from the pox infection of a cow, smallpox could be prevented.

在正痘病毒属还有另外几种病毒对人具有一定的感染性，如痘苗病毒、牛痘病毒和猴痘病毒。

Variola virus belongs to the genus of orthopoxvirus, and there are some other infectious members, such as Vaccinia virus, cowpox virus, and monkeypox virus.