Omicron has a new variant and learned the skills of Delta

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Recently, another new variant of Omicron, BA.2.12.1, became popular worldwide.

According to the phylogenetic tree analysis, the appearance time of BA.2.12.1 should be from the end of 2021 to the beginning of 2022, and the place of appearance is likely to be the United States. As of April, 97% of the BA.2.12.1 sequences uploaded globally are from the United States.

The U.S. Centers for Disease Control and Prevention said that the Omicron BA.2.12.1 mutant strain is becoming more and more common in the United States, and relevant data from the U.S. Centers for Disease Control and Prevention shows that currently about one-fifth of COVID-19 cases in the United States are caused by BA. .2.12.1 infection, in New York, New Jersey and Connecticut, confirmed cases caused by the BA.2.12.1 mutant strain of Omicron have accounted for 52.3% of the total number of new COVID-19 cases.

The BA.2.12.1 variant has also been detected in the UK, Australia, Israel, Denmark and Austria.

On May 16, the weekly report of the China Center for Disease Control and Prevention also reported that the first confirmed case of the Omicron subtype strain BA.2.12.1 appeared in China, which was imported from abroad.

The reason why BA.2.12.1 has attracted much attention lies in the two new mutation sites on its spike protein. The spike protein is an important structure for the COVID-19 virus to bind to human cell receptors and enter host cells. Because the spike protein is also the target of neutralizing antibodies and T cells, the positive selection pressure of the spike protein is particularly high, and the mutation is frequent.

The two new mutation sites on the BA.2.12.1 spike protein are S704L and L452Q, respectively. As far as L452Q is concerned, the full meaning of L452Q is that the leucine at site 452 of the spike protein is mutated to glutamine. Among them, 452 refers to the position of the spike protein, and the two letters L and Q refer to the corresponding amino acid. The protein is composed of 20 kinds of amino acids, among which L means that the amino acid before mutation is leucine, and R represents that the amino acid type after mutation is glutamine.

Indeed, mutations at the L452 position of the spike protein have been previously seen in many other variants, including Delta, Epsilon, Lambda. It is worth noting that L452 is also the most critical mutation site of the Delta mutant strain. L452 gives Delta a transmission advantage, while the original Omicron strain does not have this mutation . As a common mutation, the mutation gives the coronavirus an important functional advantage -- easier attachment to human cells.

According to the US CDC, some early evidence in the United States indicates that BA.2.12.1 has stronger immune evasion and faster transmission than BA.1/BA.2. Omicron is considered to be the most infectious COVID-19 mutant strain to date, and BA.2.12.1 is the next generation of the BA.2 mutant strain. BA.2 spreads at least 30% higher than BA.1. According to CNN, the transmission power of BA.2.12.1 is estimated to be 23% to 27% higher than that of its predecessor, BA.2.

According to the research of Xie Xiaoliang's team of Peking University, BA.2.12.1 has stronger receptor affinity than BA.1 . Compared with BA.2, BA.2.12.1 showed stronger neutralizing antibody escape ability to the sera of subjects who had been vaccinated with three doses of vaccine.