Xinhua News Agency, Beijing, January 27 (Reporter Luo Guofang) In recent weeks, the number of cases of BA.2 infection of the subtype variant strain of the Omikron strain reported by many countries has gradually increased, which is known as the "stealth Omikron". What are the characteristics of this mutant strain of ?

Will it replace the original Omicron strain and take the world by storm?

　　The genetic lineage name of the Omicron strain is B.1.1.529, and this variant strain was first identified in South Africa on November 9, 2021.

On November 26 of the same year, the World Health Organization listed B.1.1.529 as a mutant strain of "requiring attention" and named it after the Greek letter "Omicron" (Ο).

　　According to the WHO's official website, the Omicron strain includes the B.1.1.529 lineage and its descendant lineages BA.1, BA.1.1, BA.2 and BA.3.

So far, BA.1 infection cases account for the vast majority of Omicron infection cases in the world. The evidence that the Omicron strain "requires attention" is based on the genetic sequence of BA.1.

However, the number of infections with BA.2 strains with multiple different mutations in the BA.1 genome is increasing in many countries.

　　According to Pango, an international public platform for classifying and naming the genetic lineage of the new coronavirus, the genome of the BA.2 strain was first discovered in a sample submitted to the "Global Initiative for Influenza Data Sharing" platform on November 27, 2021. Collected on 17 November 2021 from Gauteng, South Africa.

　　According to a report released by the WHO on the 21st, the proportion of BA.2 strain infections in India, South Africa, the United Kingdom, Denmark and other countries is increasing.

According to foreign media reports, since November 17, 2021, about 40 countries and regions around the world have submitted a total of nearly 15,000 BA.2 strain genome sequences to the "Global Initiative for Influenza Data Sharing" platform.

　　The bulletin issued by the Danish National Serum Institute on the 20th said that the BA.2 strain is rapidly replacing the BA.1 strain in the country.

In the last week of 2021, the BA.2 strain accounted for 20% of all confirmed cases of Covid-19 in Denmark, and by the second week of 2022 this proportion had risen to 45%.

　　According to a statement issued by the British Health Security Agency on the 21st, the BA.2 strain has been identified by the agency as a "variant strain under investigation (VUI)".

As of the 21st, more than 400 cases of BA.2 strain infection have been confirmed in the UK through whole genome sequencing.

The earliest case detected so far in the country dates back to December 6, 2021.

BA.1 remains the predominant strain circulating in the UK, with BA.2 currently accounting for a very low proportion of infections.

　　The characteristics of BA.2, such as its ability to spread, are being studied and analyzed, but are not yet clear.

According to the World Health Organization, the genetic sequence of the vast majority of Omicron strains carries a mutation in which the spike protein gene segment is deleted. Infections are distinguished.

However, the genome of BA.2 does not have the deletion of this gene segment, so it cannot be found in routine Omicron infection screening, thus earning the name of "stealth Omicron".

　　The UK Health Security Agency said it was unclear what the impact of the changes in the BA.2 strain's genome would have.

Preliminary evidence suggests that the number of infected cases may be increasing faster in BA.2 than in BA.1.

There is currently insufficient evidence to determine whether BA.2 causes more severe disease than BA.1.

　　According to the Danish National Serum Institute, a preliminary analysis showed no difference in the rate of hospitalization between the BA.2 and BA.1 strains.