Analyses of infection rates in modern seasonal flu epidemics suggest that with age comes a subtle buildup of immunity to flu viruses in general.

近年来对季节性流感流行的感染率分析表明，一般而言，随着年龄的增长，针对流感病毒的免疫力也在日积月累地加强。

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Pregnant women face an increased risk even during outbreaks of seasonal influenza. But the new H1N1 flu has been affecting a younger age group than seasonal flu epidemics.

即使在季节性流感爆发的时，孕妇面临的风险就已经增加了。但是，新出现的。

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If only we could develop a vaccine that was effective against all strains of flu, we might prevent both annual epidemics and occasional pandemics like the one now under way.

如果我们能研制一种对所有流感病毒株都有效的疫苗，我们就可以预防年度季节性流感及偶见的流感大流行，就像其它那些疾病一样。

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But the new H1N1 flu has been affecting a younger age group than seasonal flu epidemics.

VOA: special.2009.08.05

But the H1N1 flu has been affecting a younger age group than seasonal flu epidemics.

VOA: special.2009.08.18

"Spanish Flu" is far from a footnote in history for scientists trying to protect us from future flu epidemics.

BBC: Flu virus victims list from 1918

When he was manager of the Vicks VapoRub brand in India, flu epidemics posed absurd dilemmas: should he boost production beyond licensed limits (a punishable offence) or leave market demand unsatisfied?

ECONOMIST: India��s choices

It is this continual process of genetic drift gives rise to the seasonal epidemics of flu and norovirus.

BBC: Winter bugs: A yearly battle for dominance