The findings, published in the journal Science, showed that the strains in circulation early in life - most people have had flu by the age of five - have a profound impact on which types of flu they would be more sensitive to in the future.
该研究发表在《科学》杂志上，结果显示（大多数人五岁前得过流感）在人们儿时传播的流感很大程度影响了他们未来对哪类流感更为敏感。

"The (first virus you encounter) seems to set you up for life to be quite good at protecting yourself, not just against that particular virus, but also close cousins of that virus," said Worobey.
伍罗贝称，“你感染的第一种流感病毒似乎不仅能使你对其终身免疫，也能抵御其他类似病毒。”

The scientists also studied two bird flu viruses, H5N1 (belonging to the type 1 branch) and H7N9 (type 2), each of which already has caused hundreds of cases of severe illness or death in humans. Scientists are concerned that in the future either of these strains could gain mutations that allow them to not only jump from birds into humans, but also spread rapidly between people, triggering a deadly pandemic.
科学家们对H5N1型（属于1型分支）和H7N9型（2型）禽流感病毒进行了研究，目前已有数百人因此患重病或死亡。科学家们担心，这类病菌未来可能发生突变，不仅能通过禽类传染给人类还可在人类之间迅速传播，导致致命流感大面积传播。

They found that if a person's first flu infection belonged to the same branch as the avian strain, they had a 75% reduced chance of hospitalisation and about an 85% smaller chance of dying.
研究发现，如果一个人首次感染的流感病毒与禽流感病毒同属一个分支，那么他们住院治疗的几率能减少75%，且死亡几率减少85%。

The findings explain the surprising observation that H5N1 tends to cause far more mortalities in younger people - contrary to what might be expected, while H7N9 tends to be most devastating in the elderly population.
研究结果说明，H5N1病毒在年轻人中的致死率更高，这一惊人发现与人们的预测恰恰相反，而H7N9病毒通常对老年人杀伤力更强。

"We're not a completely blank slate when it comes to how susceptible we are to these emerging flu viruses," said Worobey. "Even if we've never been exposed to H5 or H7 viruses, we have some kick-ass protection against one or the other."
“我们对这些新兴流感病毒并非完全没有抵抗力。即使从没有接触过H5或H7型流感病毒，我们也对其中一种有强大的抵抗力。”

This happens, he said, because when a person is infected by flu, their original antibodies are woken up as the body's first line of defence, meaning if they are poorly-matched they will be less efficient at attacking the virus.
他说，之所以会这样是因为当人们感染流感时，其原始抗体作为身体的第一道防线会被唤醒，这意味着如果抗体与病毒不匹配，那么对病毒的攻击便不太有效。

Previously, people had put these patterns down to younger people being more likely to encounter birds, or the virus being more aggressive in elderly people.
过去人们认为，发生上述模式是因为年轻人更容易感染禽流感，或禽流病毒对老年人的攻击力更强。

The scientists said it was not yet clear whether current childhood flu vaccines - which tend to involve components from both branches - would mean in future children would have higher protection against flus of both types.
科学家们称，尚不清楚当下常包含两种流感病毒免疫成分的儿童流感疫苗是否意味着孩子们将来对两种类型的流感具有较强的抵抗力。

Vocabulary
pandemic:(疾病)流行性的；传染于(全国、全洲、全世界)的
susceptible: 易受感染的
英文来源：卫报
翻译：董静（中国日报网）