The infection generates weak or incomplete immune protection, however, and humans get reinfected throughout their lives.

然而，这种感染会产生微弱或不完全的免疫保护，人类在一生中会再次感染。

It was based on some evidence that immune protection against severe disease wanes over time in these groups.

这基于某些证据显示，上述人群对抗重症的免疫保护随时间减退了。

But neither approach includes immune protection.

但这两种方法都缺乏免疫保护。

Using historical data on seasonal flu strains, Dr Worobey's team estimates that most people born before 1968 may have this type of immune protection against H5N1.

Worobey 博士的研究小组利用季节性流感病毒株的历史数据估计，大多数 1968 年之前出生的人可能具有这种针对 H5N1 的免疫保护能力。

Scientists are concerned by the number of mutations and the fact some of them have already been linked to an ability to evade existing immune protection.

科学家们对突变的数量以及其中一些突变与逃避现有免疫保护的能力有关这一事实感到担忧。