它们可以产生足够多的新病毒来训练免疫系统杀死并记住它们，所以人们只需要接种一次疫苗。
They can produce enough new viruses to train the immune system to kill and remember them, so people only need to take the vaccine once.
当人们对流感病毒没有预先免疫性，他们就需要几周间隔的两次注射而不是一次注射-这在当时免疫接种很多人去保护他们操作是非常困难的。
When people have no pre-existing immunity to a flu virus, they need not just one but two doses of vaccine several weeks apart - making it very hard to immunise many people in time to protect them.
据估计，一次大规模免疫接种运动，如果得到及时实施，可预防70%的病例。
It is estimated that a mass immunization campaign, promptly implemented, can prevent 70% of cases.
约两个月前，他们接受了第一次甲流疫苗接种；21天后，超过85%的志愿者对这种新型流感病毒菌株显示出了免疫力。
They got their first shot to test the vaccine about two months ago, and, after 21 days, more than 85 percent showed an immunity to this novel flu strain.
一定保证幼犬做过蛆虫，而且在你买回家前至少接种一次免疫。
Be certain that the puppy has been examined for worms and that it will receive at least one vaccination before it goes home with you.
一次接种的有效免疫期达6个月；
The immune duration could reach 6 months by one vaccination.
这次接种活动将是世界上最大规模的一次接种活动，将有约1亿儿童接受免疫。
This campaign will be the largest ever held in the world, and will target approximately 100 million children.
这次接种活动将是世界上最大规模的一次接种活动，将有约1亿儿童接受免疫。
This campaign will be the largest ever held in the world, and will target approximately 100 million children.
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