In recent weeks, many countries have reported the subtype variant of Omicron virus, BA 2. The number of infection cases is gradually increasing. What are the characteristics of this mutant strain known as "invisible Omicron"? Will it replace the original Omicron strain and sweep the world? The genetic pedigree name of Omicron strain is b.1.1.529. This variant strain was first confirmed 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 variant strain "requiring attention" and used the Greek letter "Omicron"（ Ο） Naming. According to the official website of who, the Omicron strain includes b.1.1.529 lineage and its offspring lineage 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 Omicron virus "needs attention" is based on BA 1 gene sequence. However, with BA There are many different mutations in Ba The number of cases infected with strain 2 is gradually increasing in many countries. According to Pango, an international public platform for the classification and naming of COVID-19 genealogy, BA. The genome of strain 2 was first found in a sample submitted to the global initiative for influenza data sharing platform on November 27, 2021. The sample was collected from HOTEN Province, South Africa on November 17, 2021. According to the report released by who on the 21st, BA in India, South Africa, the United Kingdom, Denmark and other countries The proportion of virus infection is increasing. According to foreign media reports, since November 17, 2021, about 40 countries and regions in the world have submitted nearly 15000 Ba to the "Global Initiative for influenza data sharing" platform Genome sequence of strain 2. The Danish National Institute of serum said in a communique released on the 20th that ba Strain 2 is rapidly replacing ba The 1 strain is spreading in the country. In the last week of 2021, BA The infection cases of strain 2 accounted for 20% of all newly confirmed cases in Denmark. By the second week of 2022, the proportion had risen to 45%. According to a statement issued by the British health and safety authority on the 21st, BA 2 strain has been identified as "variant strain under investigation (VUI)" by the Bureau. As of the 21st, more than 400 cases of Ba have been confirmed by whole genome sequencing in the UK 2 virus infection cases. The earliest cases found so far in the country can be traced back to December 6, 2021. BA. 1 is still the main strain transmitted in the UK, BA At present, the proportion of infection cases is very low. BA. The propagation ability and other characteristics of 2 are being studied and analyzed, which is not clear so far. According to the who, the vast majority of Omicron strains carry a mutation with a deletion of spike protein gene segment. Screening for this specific mutation can quickly distinguish Omicron infection from other variant coronavirus strains. However, BA There is no deletion of this gene segment in the genome of 2, so it can not be found in routine Omicron infection screening, so it is known as "invisible Omicron". The British health and safety agency said it was unclear What effects will the changes in the genome of strain 2 have. Preliminary evidence shows that with BA 1 compared to ba The number of infected cases may increase faster. There is not enough evidence to determine ba 2 will it be better than ba 1 cause more serious diseases. According to the Danish National Serum Institute, preliminary analysis shows that ba 2 and ba There was no difference in the hospitalization rate of patients caused by strain 1. (Xinhua News Agency)