See WHO’s Safety of COVID-19 Vaccines explainer and Vaccines Safety Q&A to learn more about common side effects and find out who should consult with a doctor before vaccination.
11032
疫苗剂量
Vaccinedoses
11033
对于一些COVID-19疫苗，需要接种两剂。
For some COVID-19 vaccines, two doses are required.
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如果需要两剂疫苗，则接种第二剂非常重要。
It’s important to get the second dose if the vaccine requires two doses.
11035
对于需要接种两剂的疫苗，第一剂是首次为免疫系统提供抗原（刺激产生抗体的蛋白质）。
For vaccines that require two doses, the first dose presents antigens – proteins that stimulate the production of antibodies – to the immune system for the first time.
11036
科学家称之为启动免疫反应。
Scientists call this priming the immune response.
11037
第二剂起到了增强的作用，确保免疫系统产生一种记忆反应，在免疫系统再次遇到这种病毒时能够抵御病毒。
The second dose acts as a booster, ensuring the immune system develops a memory response to fight off the virus if it encounters it again.
11038
由于迫切需要COVID-19疫苗，候选疫苗的初步临床试验是在尽可能短的时间内施打两剂疫苗的。
Because of the urgent need for a COVID-19 vaccine, initial clinical trials of vaccine candidates were performed with the shortest possible duration between doses.
11039
因此，世卫组织建议施打间隔为21至28天（3至4周）。
Therefore an interval of 21–28 days (3–4 weeks) between doses is recommended by WHO.
11040
现有证据表明，根据疫苗的不同，间隔可以延长到42天，有些疫苗甚至可以延长到12周。
Depending on the vaccine, the interval may be extended for up to 42 days – or even up to 12 weeks for some vaccines – on the basis of current evidence.