A prophylactic agent, device, or measure, such as a vaccine or drug.
预防剂预防性的物质、器具或措施，比如疫苗或药物
The vaccine was used to protect the whole population against infection.
这种疫苗用以为全体居民预防传染病.
The search for a new vaccine took priority over all other medical research.
在各种医药研究中, 应首先解决寻找新疫苗的问题.
