新冠肺炎疫情在全球范围内继续蔓延，每天仍有数万人被确诊感染了这一疾病。 在这场人类战“疫”的艰苦斗争中，疫苗被寄予了厚望。 但是我们何时能等来新冠肺炎疫苗呢？ As the COVID-19 pandemic sweeps the world with hundreds of thousands of new infections reported every day, many have turned to the prospect of a vaccine, but how soon can we have one? 世界卫生组织此前曾表示，新冠肺炎疫苗研制至少还需要12至18个月的时间。 According to the World Health Organization (WHO) last month, a COVID-19 vaccine is still at least 12 to 18 months away. 面对持续肆虐的疫情，不少人觉得18个月还是太长了。但对于一种新疫苗来说，18个月的研发周期其实已经是非常快的速度了。 Eighteen months might sound a long time for the still-escalating pandemic, but it is already considered a breakneck speed for launching a new vaccine. 根据以往的经验，研发一种全新的疫苗通常需要8至20年的时间。 Based on past experience, it usually takes eight to 20 years to develop a new vaccine. 一些流行病甚至在疫苗研发完成前就已经结束。比如当年“非典”疫情被有效控制后，“非典”疫苗的相关研发项目也停止了。 Some epidemics ended before vaccine development was complete. For example, work on SARS vaccines was canceled after the outbreak was contained. 此次新冠病毒爆发后，疫苗的研究速度有了很大突破。这要得益于1月初中国科学家及时分离鉴定出病毒毒株并和世界各国科学家共享了病毒基因组序列。 But the process has been greatly accelerated this time, thanks largely to Chinese scientists who successfully sequenced the genome of the novel coronavirus and shared it with the world in early January. 根据世界卫生组织统计显示，目前至少有60个新冠肺炎疫苗的研发项目，有一些已经开始进入动物试验阶段。世界各国的科研人员也在不断加入这场科学和病毒间的赛跑，加紧研发疫苗。 The WHO has highlighted at least 60 COVID-19 vaccine candidates, with many having started animal tests. Researchers around the world have also joined the race. 3月16日，两个科研团队分别启动了新冠肺炎疫苗的临床试验。此时，距离报告第一例新冠肺炎确诊病例，不到四个月的时间。 Two most advanced candidate vaccines entered clinical trials on human bodies on March 16 – fewer than four months after the disease was first reported. 在新冠肺炎疫苗的研发过程中，采用了不同的方法。 一般情况下，疫苗由不具有致病性的、已经死亡的病原体或毒性降低后的病原体制成。这两种疫苗被称为灭活疫苗和减毒活疫苗，它们能够激发较强的保护性免疫反应。 Different approaches are adopted to develop a vaccine for the novel coronavirus. Traditionally, vaccines are made with dead or weakened forms of the pathogens so that they cannot cause diseases. They are called inactivated vaccines and live-attenuated vaccines, which elicit strong protective immune responses. 还有一种疫苗被称为亚单位疫苗，这是一种从病原体中筛选出具有免疫活性片段制作而成的疫苗。与灭活疫苗和减毒活疫苗相比，亚单位疫苗副作用较少，但是对免疫系统的刺激较弱，需要与辅助性佐剂合用才产生较好的效果。 Another common type, subunit vaccines, contain selected pieces of the pathogen as antigens instead of the whole pathogen. They cause less adverse reactions than inactivated vaccines or live-attenuated vaccines, but are often less effective so they require booster shots. 除了上述几种疫苗制作方法，新冠肺炎疫苗还采用了一些新的研发方法，引起了广泛关注。 All three types are under development for COVID-19 vaccines. But it is the newer approaches that are in the spotlight this time. 此次进入临床试验阶段的两大疫苗，一个是由中国研制的腺病毒载体疫苗 “Ad5-nCoV”，另一个是由美国生物技术公司Moderna研制的信使核糖核酸疫苗“mRNA-1273”。 Among the two vaccines that entered Phase I clinical trials, one is in China with a recombinant adenovirus vector-based vaccine (Ad5-nCoV), while the other is an mRNA vaccine (mRNA-1273) by Boston-based biotechnology company Moderna. 据医学专家介绍，核酸疫苗在获得病毒基因序列后就可以体外合成，省去病毒分离、培养以及纯化、灭活等一系列流程，最大限度的压缩疫苗研发制作所耗费的时间，较传统疫苗更具有优势。 不过，此前核糖核酸（RNA）或脱氧核糖核酸（DNA）疫苗虽可用于动物防疫领域，但尚未被批准用于人类。 Experts say nucleic acid vaccines have the advantage of a shorter development and production cycle, as they use a copy of the genetic code of the pathogen without needing live virus samples. But neither RNA or DNA-based vaccines have ever been approved for use in humans before. 中国研发的腺病毒载体疫苗也具有广阔的应用前景。2017年，中国曾运用腺病毒载体技术成功研制了埃博拉病毒疫苗。 China's Ad5-nCoV is also a promising candidate, as the method was used by the same team to successfully develop an Ebola vaccine in 2017. 伴随着国际疫情的严峻形势，有专家提醒新冠肺炎可能会成为季节性疾病，再度袭来。面对病毒可能“卷土重来”的情况，研制疫苗用于防治疫情显得尤为重要。 但不管采用何种疫苗研制方法，为了疫苗的安全有效，临床试验是必不可少的关键一环。 As the pandemic continues wreaking havoc on many countries, there is a strong chance that the novel coronavirus could return in seasonal cycles. If that is the case, a reliable vaccine is the ultimate solution for the world. But no matter which approach is adopted, clinical trials cannot be skipped or hurried so as to ensure the safety and effectiveness of a new vaccine. 推荐阅读：