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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However, a child below the age of 10 will need two doses of the H1N1 vaccine, spaced about a month apart, and full immunity will not occur until about a week after the final dose.

但是，10岁以下儿童将需要两剂疫苗，期间相隔一个月，完全的免疫力将直到接种最后一剂疫苗后约1周才会产生。

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Bacteria become active as a result of anything that can reduce the person's immunity, such as HIV, advancing age, or some medical conditions.

由于可降低人的免疫力的任何东西，例如艾滋病毒、年龄增长或某些医学病症，细菌变为活动性。

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Director of the Public Health Agency Dr Caroline Harper said this age group was vaccinated last year and now 50-60% had built up some level of natural immunity.

BBC: Health Committee