当然，问题在于他们并不是免疫者。
这只是对我们的免疫系统试图防御的潜在外来入侵者的分类介绍。
Just an introduction to the classes of potential foreign invaders that our immune system tries to defend us against.
每年有许多人因季节性流感患病和死亡，尤其是老年人、2岁以上的儿童以及患有其它病症或免疫系统受损者。
Every year many people suffer and die from seasonal influenza, particularly the elderly, children younger than age 2 and people with other medical conditions or weakened immune systems.
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