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.
根据现有的资料还不足以确定初免者以及与之相对的经过很长一段间隔时间后再次接种疫苗者的不良反应发生率。
Current data are insufficient to define the incidence of adverse events in primary vaccinees as opposed to individuals re-vaccinated after a long interval.
EMEA建议人们应该有两次接种机会，中间间隔三个星期。
The EMEA is recommending that people should be given two shots, at an interval of three weeks.
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