[求助]这句话怎么理解呢?

eachjun

Poliomyelitis，for example，emerged as an epidemic in the United States in the twentieth century by then，modern sanitation was able to delay exposure to polio Until adolescence or adulthood，at which time polio infection produced paralysis． Previously, infection had occurred during infancy, when it typically provided lifelong immunity without paralysis．

例如小儿麻痹,在20世纪那时在美国是一种流行病.现代医疗设备把这个病推迟到青春期或者成年时.在这时感染可以得上麻痹.以前在婴儿期感染上,可以提供终身的免疫.

这是我对这段英文的理解.但感觉有点迷惑"现代医疗设备把这个病推迟到青春期或者成年时.在这时感染可以得上麻痹"那现代医疗有什么用?是不是那块我理解不对?越看越不明白,请高人指点,谢谢

eachjun

自己顶,谁能帮忙翻译一下呢?自己能力有限....