教训：甲流病毒似乎存在交叉保护的作用：虽然甲流对人体免疫系统是一件新鲜玩意儿，但六旬以上的老人却不容易感染，原因是此前另一种病毒肆虐过，让老人的免疫系统能抵御住甲流。

However, there seems to be some natural cross-protection going on with this virus: Though new to human immune systems, it doesn't seem to infect people over 60 very often.

youdao

教训：甲流病毒似乎存在交叉保护的作用：虽然甲流对人体免疫系统是一件新鲜玩意儿，但六旬以上的老人却不容易感染，原因是此前另一种病毒肆虐过，让老人的免疫系统能抵御住甲流。

However, there seems to be some natural cross-protection going on with this virus: Though new to human immune systems, it doesn't seem to infect people over 60 very often.

youdao