naturally acquired immunity

例句：

1. 1.The vaccine is designed to naturally acquire immunity against the virus.
   该疫苗旨在自然获得对病毒的免疫力。
2. 2. The immune system naturally acquires immunity to certain diseases.
   免疫系统自然获得对某些疾病的免疫力。
3. 3. The natural immunity of the population was a significant factor in the outbreak.
   人口的自然免疫力是疫情爆发的一个重大因素。