牛痘苗

例句：

1. 1. The vaccine is effective against the virus that causes encephalitis in cattle.
   这种疫苗对引起牛脑炎的病毒有效。
2. 2. The vaccine has been shown to be safe and effective for humans.
   这种疫苗已被证明对人类是安全的和有效的。
3. 3. The vaccine is being used to prevent the spread of the disease among humans.
   这种疫苗正在被用来防止疾病在人类之间的传播。