新冠疫苗:接种近两月 尚未解答的四个问题

BBC 02-28

这是一场跟时间的竞赛,全球的科学家医学家和公共卫生专家动员起来为全人类注射新冠疫苗,让我们的生活能够尽快恢复正常。

新冠疫苗开始注射到现在已经快要两个月,目前全世界已有6000万人口接受了疫苗接种。

但是在各国加速接种的同时,我们对新冠疫苗还是有一些尚未解答的问题,其中甚至有些很基本的问题我们都不清楚。

1. 疫苗的免疫力能维持多久?

感染过新冠病毒或者接种新冠疫苗之后,免疫力能维持多久是我们一直在寻找答案的问题。

在新冠病毒疫情爆发一年之后,有关中期和长期免疫力的第一份研究报告已经发表。

根据美国加州的拉霍亚免疫学研究所(La Jolla Institute for Immunology)的研究,新冠病毒感染者在痊愈之后,其免疫力能维持至少6个月。

这和英格兰公共卫生机构(Public Health England)的发现大致相同,该机构表示大多数病人康复后免疫力能维持至少5个月。

考虑到新冠病毒疾病还是一年前才出现的流行病,科学家相信免疫力应该能维持更长的时间,甚至长达数年之久。

疫苗提供的免疫力也大致相同,但每个人身体体质不同,也许有些人免疫力能维持更久,有些人免疫力维持更短。

英国莱斯特大学病毒学家朱利安·唐(Julian Tang)表示,“疫苗接种工作才刚开始,现在很难断定免疫力能维持多久,大概是介于6至12个月之间,但是有很大一部分取决于病人本身,以及疫苗的种类。”

美国梅奥诊所医学中心(Mayo Clinic)的分子医学教授巴德利(Andrew Badley)更为乐观,“我相信疫苗的效用和免疫力可能持续几年。详细分析感染变异毒株的病例和患者接种后的反应也非常重要。”

2. 接种疫苗后还会感染新冠病毒吗?

严格来说,这是有可能的。

首先,大部分的疫苗要等到接种二至三周之后才会产生保护力,如果在接种疫苗的第二天,或是一周后暴露在新冠病毒下,还是有可能会被感染的,而且还会传播病毒给其他人。

就算是在接种疫苗数周之后再暴露在新冠病毒下,也不能说绝对不会被感染。

美国梅奥诊所医学中心(Mayo Clinic)的分子医学教授巴德利(Andrew Badley)表示,现有的数据显示,一些接种过疫苗的人还是会感染新冠病毒,但是比起没接种疫苗的人,他们体内的病毒量比较少,病情也更加轻微,传播病毒给其他人的机会更小。

医学界目前的共识是,不论是哪一种疫苗,都能够保护绝大多数的人,但是保护免于感染和散播病毒的程度如何还很难下定论。

3. 疫苗对新冠病毒变异毒株也有效吗?

这是许多人关切的问题之一,病毒一直在不停改变适应环境,有时候是因为抵抗疫苗而出现变异。

英国和南非出现的新冠病毒变异毒株已经散播到其他国家,而且因为传染力更强而更难以对付。

莫德纳疫苗已经表示,疫苗对英国和南非新出现的变异病毒仍然有效,但他们会研发新疫苗成分提高保护力。

辉瑞/BioNTech疫苗也表示能有效对抗新变异毒株,但是巴德利教授表示,没有100%有效的疫苗,疫苗的保护程度要看病毒的变异情况。

总结来说,各国政府和公共卫生机构将持续观察,密切注意是否有新变异病毒株出现,并评估现有治疗方法和疫苗是否有效。

4. 需要在多长时间里,接种多少剂量?

举例来说,辉瑞/BioNTech、莫德纳和牛津/阿斯利康等三种疫苗,都需要分别接种两个剂量的疫苗。

在一开始,根据不同疫苗的测试情况,人们被告知需要在接种第一剂疫苗的3至4个星期之后,接种第二剂疫苗。

但是在2020年底,英国政府宣布将首先扩大第一剂疫苗的接种,让尽可能多的人先接种第一剂疫苗,然后在3个月之后接种第二剂疫苗。

英国政府的做法在国际上引起很大的讨论,但是辉瑞和大多数的科学界人士仍然表示需要按照临床测试验证的方式进行疫苗注射,也就是第一剂和第一剂相隔21天。

世界卫生组织也做出建议,认为两剂疫苗之间最好只相隔21天或28天,在特殊情况下最多拉长到6个星期。

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