However, the author has not seen strong evidence to confirm this statement so far. Major media have also invited many experts to explain, and they all said that this statement is not credible. Experts said that XBB1.5 will indeed lead to an increase in the number of infections, but its pathogenicity is not significantly different from the previous Omicron strain .
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But it must be said that XBB1.5's ability to spread and infect is indeed quite violent. In the previous week, it had accounted for 40.5% of the new crown cases in the United States, making it the number one epidemic strain. This shows that it must have a powerful trick. Why does the new coronavirus mutate so quickly and produce poisonous kings like XBB1.5? Will it become popular in China?
With these questions, let’s first understand the production process of XBB1.5. It is also called XBB.1.5, which evolved from XBB, a sub-branch of Omicron , so whether it is XBB or XBB1.5, it belongs to the large category of Omicron, and is not a new branch that does not belong to Omicron.
XBB still belongs to the Omicron family
Since its emergence, the new coronavirus has been mutating all the time. This is because it is a single-stranded RNA virus, and genetic information is all stored on one RNA strand. The structure of the new coronavirus is very simple, consisting of a protein coat wrapping RNA genetic material. Compared with double-stranded DNA, single-stranded RNA is unstable during the replication process, and errors often occur, leading to mutations.
The structure of the new coronavirus has a single-stranded RNA molecule on the inside and a protein shell on the outside
The direction of these mutations is random. Many mutant strains have disappeared directly because they cannot replicate or cannot adapt to the environment. After a large amount of screening, only some mutant strains can survive, and even fewer of them will replace the previous strains and become dominant strains. From the current point of view, strains with weaker pathogenicity and more contagiousness are more likely to become dominant strains.
This can be explained by a cruel principle of natural selection. Those highly pathogenic mutant strains cause severe symptoms and high mortality, which in turn reduces the ability of patients to move around and spread the virus . Mutants with low pathogenicity cause milder symptoms and have less impact on the patient's mobility, so they have stronger transmissibility.
The genetic material of the virus is stored in RNA molecules
And in terms of infectivity, it is even simpler. Of course, highly infectious strains will more easily become dominant strains. Combining these two items, it is not difficult to find that after more than three years of mutation, the general trend of the new coronavirus is that its pathogenicity is getting weaker and weaker, while its contagiousness is getting stronger and stronger.
There are currently more than 130 mutant strains of the new coronavirus. From the perspective of mutation routes, they are mainly divided into several large branches, including the original strain, Alpha, Beta, Gamma, delta, Omicron, etc. Among them, the Omicron branch is the most contagious and relatively weak in pathogenicity, thus quickly defeating other branches and becoming the main strain prevalent in the world.
Omicron's mutation route
Omicron was first discovered in South Africa and Botswana . Compared with the original strain, it has more than 60 mutation sites, 37 of which are located on the spike protein of the virus. The spike protein is a spike-like protein that protrudes from the virus shell, also known as the S protein. This protein can bind to the ACE2 receptor in human cells and is the key for the virus to invade the human body.
Omicron has a large number of mutations on the spike protein that make it easier to bind to the ACE2 receptor, making it very contagious.In addition, Omicron can also escape the humoral immune barrier established by the vaccine or previous infection with other mutant strains, which means it has a stronger immune evasion ability.
The virus spike protein binds to the cellular ACE2 receptor
With these advantages, Omicron has become the well-deserved king of the new coronavirus. Although its pathogenicity is weak, due to its extremely strong transmission ability, the number of infections has doubled, and the total number of deaths is actually more than that of other branches. After the emergence of Omicron, the virus did not stop mutating. Following Omicron's successful route, new mutant strains with stronger infectivity and immune evasion capabilities continued to emerge, forming a huge Omicron family.
The viral spike protein binds to the cellular ACE2 receptor
Currently popular in my country are mainly the BA.5.2 and BF.7 branches of this family, but these mutant strains are no longer the dominant strains abroad. Currently, the most popular strains in the United States are XBB1.5, known as "Siren", and BQ.1.1, "Cerberus". XBB1.5 has obviously overwhelmed BQ.1.1 and has gradually become the main popular strain. So why is the name XBB so strange? The X in
XBB represents "recombination", which means that this strain is recombined from two mutant strains. The two letters B represent the two recombined strains, namely BA.2.75 and BJ.1 (ie BA.2.10.1). The mutation process of the recombinant virus strain is very special. It is caused by the exchange of genetic material in the body after the same person is infected with two different new coronavirus mutant strains.
XBB is recombined from BA.2.75 and BJ.1.
XBB first appeared in India in August 2022, and was subsequently discovered in 17 countries including Australia, Bangladesh, Denmark, Japan, and the United States. The great thing about XBB is that its immune evasion ability is stronger than other Omicrons, so it is more likely to infect the human body. However, the neutralizing antibodies in people who have been vaccinated or have been infected with other strains often have no effect on XBB. This also makes XBB more likely to cause to re-infect .
But this is not over yet. On the basis of XBB and XBB.1, a more powerful XBB.1.5 (i.e. XBB1.5) has been produced. This strain has the same immune evasion ability as XBB.1, but compared with other XBB strains, an additional mutation F486P has been added, which has a stronger affinity with the ACE2 receptor of human cells, making it easier to infect the human body. It is precisely because of this mutation that XBB1.5 has an advantage in the United States and has become the new poison king in the past week.
In fact, XBB1.5 has been discovered in my country. For example, XBB1.5 cases have been detected in Shanghai, but the vast majority are imported cases from abroad and are under closed-loop independent management, so they have not caused large-scale local transmission. However, my country will relax its entry quarantine policy on January 8 and cancel nucleic acid testing and centralized quarantine for all employees after entry. Therefore, many people are worried that the introduction of XBB1.5 into the country will accelerate after January 8, thus starting to spread in the country, weakening the effectiveness of the vaccine, and causing breakthrough infections and secondary infections.
The immune evasion ability of However, considering that XBB1.5 has a stronger immune evasion ability and may trigger a new wave of infection, it must be taken seriously.
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