为何叫它BA.2.12.1？ 奥密克戎家族命名揭秘

2020年和2021年，世界卫生组织宣布新冠病毒出现了令人担忧的变异株，并用希腊字母命名它们。今年以来，奥密克戎（Omicron）家族仍然是公众关注的焦点，奥密克戎谱系下的亚变异株具备了更强的免疫逃逸能力，从而引发了新一波的感染潮。例如，奥密克戎亚体BA.2.12.1正在北美流行，而BA.4和BA.5又在南非迅速传播。

鉴于奥密克戎亚变异株的主导地位日益增强，近日《自然》杂志采访了相关研究人员，以了解目前这些名称的由来，并了解了为什么世界卫生组织没有给它们起希腊名字，从而促使决策者采取更有力的行动。

科学家如何识别病毒变异株?

新冠病毒在细胞中复制时发生突变。从技术上讲，这意味着病毒每天可能会产生数百万种变异株。但是大多数的变异株并不能提高病毒的生存和复制能力，这些变异株会随着时间的流逝而消失，被适应性更强的变异株打败。

然而，一小部分变异株确实受到了推进。当这种情况发生时，监测病毒基因组的研究人员会将样本中具有相同特定突变的一组进行标记。为了核实这些样本是否构成了新冠病毒进化树的一个新分支，他们会联系已经为病毒建立了命名系统的生物信息学家。此前，由大约24名进化生物学家和生物信息学家组成了一个名为“Pango”的组织，他们使用基因进化树软件将病毒基因组样本的序列与数百个其它样本的序列进行比较。

如果分析表明，这些新样本来自同一个新近的祖先，这意味着它们在进化树上是一个特定的谱系。在决定是否为该谱系命名时，Pango会考虑这些变异株是否随着时间的推移出现得更频繁，以及突变是否集中在病毒的某个区域，从而可能使其更具有竞争优势。在这一层面上，一个谱系的标签并不意味着风险。相反，它可以让科学家们密切关注变异株并了解更多。

英国爱丁堡大学进化生物学家、“Pango”成员安德鲁·兰博（Andrew Rambaut）说：“我们想要命名所有在早期阶段突然跳到我们面前的东西，这样我们就可以定义它，并追踪它，看看它是否相对于其它谱系生长得更快。”他说：“你可能都不会听说我们命名的大部分病毒谱系，因为它们无法与病毒的其它变异株竞争，已经消失了。”

变异株如何命名?

当命名一种变异株时，Pango委员会使用一个等级系统来表明该变异株的进化史，以及它相对于其它变异株的检测时间。名称的首字母反映了Pango何时给了这个谱系一个标签，标签的序列A到Z，然后从AA到AZ, BA到BZ，等等。后面的数字以句号分隔，表示该谱系分支的顺序。例如，BA.1、BA.2、BA.3、BA.4和BA.5是奥密克戎祖先株系的前五个分支。BA.2.12.1是从BA.2分支出来的第12个谱系，然后是第12丛上的第一个命名的分支。所有的亚变异株都是变异株，但研究人员使用之前的名称，来暗示该谱系属于一个更大的群体，例如奥密克戎。

如果一种病毒变异株相对于其它变异株，能更有效地逃逸免疫系统，导致更严重的疾病或传播能力更强，世界卫生组织可能会将其确定为一种“值得关注的病毒变异株VOC”，并将其名称改为一个希腊字母。例如，2021年被标记为B.1.1.529的一种新冠病毒变异株由于其具有多重令人担忧的突变，加上数目快速增长，世界卫生组织在2021年11月将其名称改为奥密克戎（Omicron）。虽然Pango提供的技术性名称旨在帮助研究人员跟踪新冠病毒的演变，但世界卫生组织的命名系统将与公众沟通的便利性放在了优先位置。

新冠病毒是否比其它病毒进化得更快?

兰博特说，不一定。研究人员正在发现新冠病毒惊人的多样性，但他们也在以前所未有的速度对病毒进行基因测序。自2020年1月以来，创纪录的1100万个新冠病毒基因组被上传到GISAID数据平台。相比之下，自2008年5月以来，研究人员将大约160万个流感病毒序列上传到了GISAID的EpiFlu数据库。

尽管如此，兰博特说，关于新冠病毒是如何演变，仍有许多悬而未决的问题，因为在世界上一些地区，病毒的基因组测序工作几乎没有开展，而一些疫情肆虐的国家正在缩减基因组监测工作规模。

奥密克戎的亚变异株，比如BA.4，最终会有希腊名字吗?

是的，尽管它还没有发生。一些研究人员认为，目前导致感染人群数量激增的奥密克戎亚变异株，如BA.4和BA.2.12.1，应该有更简单的名称，使得在目前口罩等防护措施减弱的情况下，政府和公众能有更好地沟通。他们还指出，不同于德尔塔的亚变异株(媒体上没有太多讨论)，BA.4和BA.2.12.1可以逃逸人群早期感染其它奥密克戎亚变异株所产生的免疫力。南非流行病响应与创新中心的生物信息学家Houriiyah Tegally建议说:“每个人都认为只有新的变异株才会引发新的感染浪潮，但现在我们看到奥密克戎的家族成员就可以做到这一点，也许我们应该调整命名系统。”

但到目前为止，世界卫生组织反对这种想法。世卫组织病毒学家洛伦佐·苏比西(Lorenzo Subissi)表示，奥密克戎亚变异株彼此之间的免疫逃逸能力并没有太大区别。他补充说，如果未来的研究证明，一种奥密克戎亚变异株相比其它亚变异株能够引起更严重的疾病，该机构的评估可能会改变。世卫组织新冠病毒应对工作的技术负责人玛丽亚·范·科克霍夫（(Maria Van Kerkhove)补充说，该机构也不建议将技术标签换成希腊名字。她说:“这已经是一种可怕的病毒，仍在不必要地夺去大量人的生命。”她表示，世界各国领导人已应对此予以关注。

In view of the growing dominance of the Omicron mutants, Nature recently interviewed researchers to understand the origin of these names and to understand why the World Health Organization did not give them Greek names, thus prompting policy makers to take stronger action.

How do scientists identify virus variants?

Novel coronavirus mutated when he replicated in the cell. Technically, this means that the virus may produce millions of mutations every day. However, most of the mutants can not improve the survival and replication ability of the virus, these mutants will disappear with the passage of time and be defeated by more adaptable mutants.

However, a small number of mutants did get a boost. When this happens, researchers who monitor the virus genome mark a group of samples with the same specific mutations. To verify whether the samples constitute a new branch of novel coronavirus's evolutionary tree, they will contact bioinformatics who have established a naming system for the virus. Previously, a group of about 24 evolutionary biologists and bioinformatics called Pango used genetic tree software to compare the sequence of viral genome samples with the sequences of hundreds of other samples.

If the analysis shows that these new samples come from the same recent ancestor, it means that they are a specific pedigree in the evolutionary tree. When deciding whether to name the pedigree, Pango considers whether these mutants appear more frequently over time, and whether mutations are concentrated in a region of the virus, which may make it more competitive. At this level, a pedigree label does not imply risk. Instead, it allows scientists to keep a close eye on the mutants and learn more.

"We want to name everything that suddenly jumps in front of us at an early stage so that we can define it and track it to see if it grows faster than other genealogies," said Andrew Rambaut, an evolutionary biologist at the University of Edinburgh and a member of Pango. "you probably won't even hear about most of the virus lineages we named because they can't compete with other variants of the virus and have disappeared," he said. "

How to name the mutant?

When naming a mutant, the Pango committee uses a hierarchical system to indicate the evolutionary history of the mutant and its testing time relative to other mutants. The first letter of the name reflects when Pango gave the pedigree a tag, the sequence of tags A to Z, and then from AA to AZ, BA to BZ, and so on. The following numbers are separated by a period, indicating the order of the pedigree branches. For example, BA.1, BA.2, BA.3, BA.4 and BA.5 are the first five branches of Omicron's ancestral strain. BA.2.12.1 is the 12th pedigree from BA.2, followed by the first named branch on the 12th cluster. All the subvariants were mutants, but the researchers used the previous name to suggest that the pedigree belonged to a larger group, such as O'Micron.

If a virus mutant can escape the immune system more effectively than other mutants, leading to more serious disease or stronger ability to spread, the World Health Organization may identify it as a "virus mutant of concern" and change its name to a Greek letter. For example, a novel coronavirus variant marked B.1.1.529 in 2021 changed its name to Omicron in November 2021 because of its multiple worrying mutations and the rapid growth in its number. Although the technical names provided by Pango are designed to help researchers track novel coronavirus's evolution, the World Health Organization's naming system gives priority to the ease of communication with the public.

Does novel coronavirus evolve faster than other viruses?

'not necessarily, 'says Rambout. Researchers are discovering novel coronavirus's amazing diversity, but they are also sequencing the virus at an unprecedented rate. Since January 2020, a record 11 million novel coronavirus genomes have been uploaded to the GISAID data platform. By contrast, researchers have uploaded about 1.6 million flu virus sequences to GISAID's EpiFlu database since May 2008.

Still, Rambout said, there are still many unanswered questions about how novel coronavirus evolved, because little work has been done to sequence the genome of the virus in some parts of the world. and some epidemic-ravaged countries are scaling back their genome surveillance efforts.

Will Omicron's Asian variants, such as BA.4, eventually have a Greek name?

Yes, even though it hasn't happened yet. Some researchers believe that Omicron subvariants, such as BA.4 and BA.2.12.1, which are currently causing a surge in the number of infected people, should have simpler names, allowing better communication between the government and the public at a time when protective measures such as masks are weakening. They also point out that, unlike Delta's subvariants (which have not been much discussed in the media), BA.4 and BA.2.12.1 can escape immunity from early infection with other Omicron subvariants. Houriiyah Tegally, a bioinformologist at the Center for Epidemiological response and Innovation in South Africa, suggested: "everyone thinks that only new mutants can trigger a new wave of infection, but now that we see that Omicron family members can do this, maybe we should adjust the naming system."

But so far, the World Health Organization has opposed the idea. World Health Organization (WHO) virologist Lorenzo Subisi (Lorenzo Subissi) said that the immune escape ability of Omicron submutants is not much different from each other. The agency's assessment could change if future studies prove that one Omicron subvariant can cause a more serious disease than other subvariants, he added. Maria van Kokhoff (Maria Van Kerkhove), the technical director of World Health Organization (WHO) novel coronavirus's response work, added that the agency also did not recommend changing the technical label to a Greek name. "this is already a terrible virus that is still killing a lot of people unnecessarily," she said. " She said that world leaders should pay attention to this.