Why does the new coronavirus keep "changing"?

  The more times the virus replicates, the more people it infects, the more likely it is to mutate and the greater the number of variants.

Omicron is like this, it can infect a large number of hosts and can coexist with hosts for a longer period of time, so people will see the existence of more Omicron variants.

  【Answer "epidemic" to solve confusion】

  ◎Our reporter Chen Xi

  Recently, the "Chinese Center for Disease Control and Prevention Weekly Report (English)" reported the specific situation of my country's first imported case confirmed to be infected with the new coronavirus Omicron subtype BA.2.12.1.

This case is an overseas passenger who entered Guangzhou City, Guangdong Province, and has been transferred to the Eighth Hospital Affiliated to Guangzhou Medical University for treatment.

  Up to now, there have been reports from many countries that Omicron subtype mutants BA.2.12.1, BA.4, BA.5 and recombinant mutants XQ, XE, XM have been found.

Omicron's continued "evolution" is troubling, so will the new coronavirus keep "changing"?

  In order to survive Omicron had to be "changeable"

  "The reason why the new coronavirus is 'changeable' is because it is an RNA (ribonucleic acid) virus." Wang Tao, a professor at the School of Life Sciences of Tianjin University, introduced in an interview with a reporter from Science and Technology Daily that RNA virus replication relies on its own RNA polymerase. This polymerase has poor error-correcting ability. If a gene mutation occurs during virus replication, the polymerase will not remove the mutated gene.

If things go on like this, the mutant genes will continue to accumulate in the RNA virus, eventually causing the RNA virus to keep mutating.

  In addition, the "fickleness" of the new coronavirus is an inevitable choice for its survival.

  A virus is a tiny organism with a very simple structure. It cannot survive alone, but must survive in the cells of other organisms, which determines that it must depend on the host's cells to survive and reproduce.

Humans are the hosts of the new coronavirus, and the mutual adaptation of the virus and the human immune system has prompted the co-evolution of the two.

  "That is to say, the interaction between the virus and the host allows them to continuously evolve and eventually survive together." Wang Tao said, "We sometimes use the arms race to describe the relationship between the two. If the human immune system is strong, it can suppress the To live in the virus, when the virus enters the human body, it will be eliminated by the immune system; in order to survive, the virus must also improve its 'armament', that is, keep mutating to adapt to the host's immunity, and then the virus can continue to replicate on the host. ."

  In this contest, sometimes humans have the upper hand, and sometimes viruses have the upper hand.

  The more infectious variant will replace the weaker

  Many people will wonder why now, apart from Omicron, few other new coronavirus variants have been heard, and it seems that only Omicron is constantly "changing".

  In this regard, Chen Chunqi, a professor at the School of Life Sciences of Hubei University, explained that the mutation of the virus has no direction and may become stronger or weaker.

The stronger virus is more harmful to the host, so it is more difficult to spread widely.

The weakened virus causes less damage to the host, and it can stay on the host for a longer time. At the same time, because it has little impact on the host and does not affect the host's activities too much, it promotes the spread of the virus in disguise.

In a way, a weakened virus is more likely to spread.

  An epidemiological study from South Africa and an epidemiological study from the United Kingdom showed that the probability of severe illness among people infected with Omicron was about 25% lower than that of Delta infection.

  Meanwhile, in another study published in the Journal of Chemical Information and Modeling, the researchers used artificial intelligence models to deeply analyze the infectivity, vaccine breakthrough, and antibody resistance of Ormicron variants.

The results show that Omicron is more than 10 times more infectious than the original new coronavirus, and 2.8 times more infectious than Delta.

  "The more times the virus replicates, the more people it infects, the more chance it has to mutate and the more variants it has. That's how Omicron is, it can infect a large number of hosts, and it can interact with the host. Longer coexistence, so people will see the existence of more Omicron variants." Chen Chunqi said, at the same time, Omicron is more infectious, and the highly infectious mutants will gradually replace the infectious weak mutants.

When the number of people infected with delta increases, more people in the population develop a protective immune response against delta, that is, herd immunity is formed, which reduces the number of delta-infected people, that is, the source of infection decreases, and it becomes more difficult to infect new hosts. As it increases, it becomes less and less and may eventually disappear.

This is also the reason why the new coronavirus mutants that appear later tend to replace the previously popular mutants.

  The rate of mutation of the new coronavirus is not fast

  In fact, not only the new coronavirus, but other viruses in nature are constantly "changing".

  Wu Guizhen, chief expert on biosafety at the Chinese Center for Disease Control and Prevention, believes that compared with other viruses, the mutation rate of the new coronavirus is not fast, and the mutation rate is "only about 1/2 that of influenza virus and 1/4 of HIV."

  "From the perspective of mutation alone, compared with other viruses, the new coronavirus does not have much advantage. However, due to its strong transmission power, the main route of transmission is through the respiratory system, which increases the difficulty of controlling the spread of the new coronavirus." Chen Chunqi further said At present, the gene mutation in the new coronavirus mainly occurs in the region of the spike protein. The new coronavirus binds to the human cell receptor through the spike protein on its surface and invades the human body.

The antibodies produced by previous infection with the new coronavirus attach to the site where the new coronavirus spike protein binds to the receptor. Generally speaking, they can block this binding. However, due to the mutation of the new coronavirus, the new mutant can use If the new method is combined with the receptor, the power of the existing immune "weapon" will be weakened, which is also the difficulty of preventing and controlling Omicron.

  In nature, there are many viruses that are more contagious than the new coronavirus, such as the measles virus.

"But the measles virus loses its transmissibility after it mutates, and it only has one host for humans. Vaccination against it is very effective." Wang Tao gave an example. Another example is the hepatitis C virus. Its mutation ability is higher than that of Omicron. However, because it can only be transmitted through blood or sex, it is far less transmitted than Omicron.

  However, the mutation of the new coronavirus still has an ultimate limit.

Alice Cazorakis, an expert on virus evolution at Oxford University, believes that the new coronavirus is unlikely to mutate into a super mutant that combines all the bad mutations.

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