guarding against a possible secondary infection

例句：

1. 1. The soldiers were guarding the border against intruders.
   士兵们在边境守卫，防止入侵者。
2. 2. The policeman was guarding the crowd during the protest.
   警察在抗议期间守护人群。
3. 3.The baby was sleeping peacefully while being guarded by a nurse.
   婴儿在护士的监护下安静地睡着。