第一次打流感疫苗的孩子要打两针：6个月至8岁、间隔至少四周
流感季已经开始，不少家长带孩子打了第一针流感疫苗，却不知道有些孩子这一季还要再打第二针。美国疾病控制与预防中心（CDC）与美国儿科学会的接种规则说得很清楚：6个月以上的人每年都应接种流感疫苗，其中6个月至8岁的孩子，如果是第一次接种流感疫苗，或者在此前总共只打过一剂，又或者接种记录不清楚，这一季需要打两剂，两剂之间至少间隔四周。
为什么第一次要打两针，是因为年幼孩子的免疫系统第一次接触流感疫苗，第一剂先让免疫系统认识病毒，第二剂再把保护力补足。只打一剂，保护并不完整。等孩子累计打满两剂以后，往后每个流感季打一剂就够了。9岁及以上的孩子，每季一剂即可。
还有一个细节容易被忽略：如果孩子在打第二剂之前刚满9岁，只要这一季本就属于要打两剂的情况，第二剂照样要打完。家长拿不准孩子以前打过几剂时，可以把接种记录带给儿科医生或接种点核对，医生会按记录判断这一季要打一剂还是两剂。
需要两剂的孩子，第一剂越早打越好，这样第二剂才能赶在流感高峰到来之前完成。6个月以下的婴儿还不能接种流感疫苗，保护他们的办法是孕妇在孕期接种，以及家人和照护者都打好疫苗。（来源：美国疾病控制与预防中心）
Children Getting a Flu Vaccine for the First Time Need Two Doses, at Least Four Weeks Apart
Flu season is under way, and many parents who have taken a child for a first flu shot do not realize some children need a second one in the same season. Guidance from the Centers for Disease Control and Prevention and the American Academy of Pediatrics is clear: everyone 6 months and older should get a flu vaccine every year, and children from 6 months through 8 years who are getting it for the first time, who have received only one dose in total before, or whose record is unknown need two doses this season, given at least four weeks apart.
The reason is how a young child's immune system learns. The first dose introduces the virus to the immune system, and the second dose builds protection up to full strength. One dose alone leaves a first-time child only partly protected. Once a child has received at least two doses in total, one dose each later season is enough. Children 9 and older need just one dose a season.
One detail is easy to miss: if a child turns 9 before the second dose, the second dose should still be given when the child was due two doses this season. Parents who are unsure how many doses a child has had can take the vaccination record to the pediatrician or clinic, who will work out whether one dose or two are needed this season.
For children who need two doses, the first should be given as early as possible so the second can be completed before flu activity peaks. Babies under 6 months cannot be vaccinated yet; they are protected when the mother is vaccinated during pregnancy and when family members and caregivers are vaccinated. (Source: Centers for Disease Control and Prevention)
来源：美国疾病控制与预防中心
发布：GSM·美国（发布链接）
图片来源：图：小学生接受流感疫苗接种（Sgt. Gerald Wilson 摄，Wikimedia Commons，公共领域）。 / Photo: A schoolchild receiving a flu vaccine, by Sgt. Gerald Wilson, Wikimedia Commons (public domain).
GSM Global · 本篇英文版 English edition of this story
