Sixty percent of the Greek letters have been used. Why has Omicron become the highest level of concern variant?

According to the announcement released by the WHO on the afternoon of November 26: The B.1.1.529 variant has been classified by the organization as the highest level "variant of concern" (VOC) and named "Omicron".

The research team of Rome Children's Hospital in Italy released the world's first picture of the new variant of the new coronavirus, Omicron

South Africa first reported the variant to the WHO on November 24, and the sample of the variant was collected on November 9. This means that the variant has been spreading around the world for at least more than 3 weeks.

After Belgium reported the first case of infection with the Omicron strain in Europe on the 26th, the United Kingdom, Germany, and Italy also reported confirmed cases on the 27th, and the Netherlands and the Czech Republic also reported related suspected cases. Confirmed cases of infection with the Omicron strain also appeared in Hong Kong, my country. Subsequently, major countries in the world took countermeasures.

To prevent the invasion of the epidemic, Israel announced on the 27th that it would close its borders and prohibit all foreign travelers from entering, becoming the world's first "country" to block its borders due to the "Omicron" strain. On November 29, Japanese Prime Minister Fumio Kishida announced that from 0:00 on the 30th, all foreigners would be suspended from entering Japan. On November 29, the United States announced that it would begin to impose travel restrictions on citizens from 8 countries including South Africa, Botswana, Zimbabwe, Namibia, and Mozambique. Why did this mutation cause panic around the world? What is the difference between "Omicron" and previous variants?

1. Why does the novel coronavirus change so quickly?

The new coronavirus (2019-nCoV) belongs to the β-coronavirus, which is an RNA virus with a relatively simple structure: protein encapsulates the genetic material RNA. One of the structural proteins is named spike protein (also known as S protein), which invades the host by binding to the cell's angiotensin-converting enzyme 2 (ACE-2).

The three-dimensional fine structure of the inactivated new coronavirus

When the new coronavirus enters our body, the RNA it carries begins to replicate crazily. The more people are infected, the more opportunities there are for replication. During the hundreds of billions of replications, the virus is very likely to make random replication errors, resulting in changes in the RNA nucleotide sequence, which is what we call mutation. The absolute value of the replication process is huge. Even if the mutation rate is very low, the accumulation of quantity can lead to a qualitative leap. When the replication errors accumulate to a certain extent, a new mutant coronavirus strain will be produced.

In fact, the mutation of the new coronavirus is not uncommon. Mutation is a universal law in the biological world, and the new coronavirus is no exception. Compared with other organisms, viruses are more likely to mutate, and RNA viruses mutate more randomly and more frequently than DNA viruses.

Any virus will mutate during its evolution, and most of them mutate in the direction of adapting to the environment, evading antibodies, and resisting drugs. Especially for RNA viruses like the new coronavirus, mutation is the norm. Continuous mutation can help it evade antibody recognition, making it more difficult for us to detect and treat.

The novel coronavirus is not only changeable, but also highly contagious. Studies have found that the novel coronavirus binds to the host cell receptor target angiotensin-converting enzyme 2 (ACE-2) with a much higher affinity than the SARS virus (>10-20 times), which means that the novel coronavirus is more contagious than the SARS virus.

2. The particularity of this mutation

Since the beginning of 2020, the new coronavirus has undergone many mutations, from Alpha to Omicron. In just over a year, more than half of the Greek letters used to name it have been used unknowingly. The rate of mutation is truly astonishing.

However, even if we count the famous Delta virus strain in the news reports, none of them caused a global epidemic prevention earthquake like "Omicron", so that Israel and Japan were forced to "close the country".

The reason why Omicron is considered a dangerous strain is that 32 mutations were found on its spike protein (S protein). In comparison, the Delta strain that has swept the world has only 16 mutations. The spike protein is responsible for recognizing and binding to receptors on the surface of host cells, playing an important role in the first step of viral infection. Except for inactivated vaccines, all vaccines currently under development use the spike protein as the main target. In the spike protein, there is a key part called RBD, which directly contacts angiotensin-converting enzyme 2 (ACE-2) on the surface of human cells and then infects human cells. The Omicron strain has 10 mutation sites in the RBD, while the popular Delta strain has 2 and the Beta strain has 3.

Comparison of spike protein mutations between Delta and Omicron strains

Therefore, it is certain that "Omicron" is more contagious than previous strains. However, its pathogenicity is still unclear at this stage. The good news is that the initial reported cases of infection in South Africa often have milder symptoms, including muscle aches, fatigue, and a slight cough, but it will still take some time to fully understand the pathogenicity of the "Omicron" strain. The mutation of the new coronavirus, especially for people with low immunity, can lead to unpredictable consequences, so prevention remains a top priority.

3. Are nucleic acid testing and vaccines still effective?

Are our two major means of combating the new coronavirus, vaccines and nucleic acid testing, still effective?

Since one of the target sequences of nucleic acid testing (RT-PCR) is the relatively conserved ORF1a/b region of the new coronavirus, mutations in the four major mutants (alpha, beta, gamma and delta) that have appeared previously do not affect nucleic acid testing.

At present, the full gene sequence of the "Omicron" strain has been made public, and no mutations that affect detection have been found in the new variant, and "Omicron" can still be detected by nucleic acid testing. Four companies, including Shuoshi Bio, Rejing Bio, Zhijiang Bio, and Dongfang Bio, have successively published articles on their official accounts, saying that their new crown reagent detection related products can effectively detect the "Omicron" variant. As for the effectiveness of existing vaccines against "Omicron", it is still impossible to draw a conclusion.

On November 28, Burton, chief medical officer of Moderna, a COVID-19 vaccine manufacturer, issued a statement that he suspected that the "Omicron" strain might evade the current vaccine. He said that the new improved vaccine might be available in early 2022. "If we have to develop a completely new vaccine, I think it will be in early 2022 before it can be mass-produced." He said: "As a non-messenger RNA (mRNA) vaccine, the strength of Moderna is that we can respond very quickly."

Burton said that the current vaccine protection against the virus should still exist, but it depends on how long ago a person was vaccinated. The best advice at present is to get the existing new crown vaccine. Although there is still uncertainty about the vaccine against "Omicron", we don't have to worry too much.

Zhang Wenhong, head of the Shanghai COVID-19 clinical treatment expert group and director of the Department of Infectious Diseases at Huashan Hospital affiliated to Fudan University, said that he believes that it will not have a big impact on China at present, and China's current rapid response and dynamic zero-clearing strategy can cope with various types of new coronavirus variants.

"No matter how the new coronavirus changes, it is still the new coronavirus. China is currently in a period of strategic opportunity won by the dynamic zero-clearing strategy. It is accelerating the construction of scientific support needed to cope with normalized anti-epidemic efforts in the next stage, including the formation of effective vaccine and drug reserves, as well as public health and medical resource reserves to support the world's openness. Based on science and solidarity, we can deal with Delta and Omicron," said Zhang Wenhong.