Omicron reproduces new variant branch CH.1.1, toxicity will become weaker and weaker?

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A new mutant branch of Omicron, CH.1.1, has begun to spread in multiple countries, and on the evening of January 31, 2023, the CDC’s official WeChat public website “China CDC News” published an article introducing CH.1.1 as a sixth-generation subbranch of the Omicron mutant strain BA.2.75, which virus experts have named “Orthrus” (a two-headed dog in Greek mythology).

CDC said that the latest research shows that CH.1.1 has increased immune escape capacity due to the addition of multiple mutant loci. Worryingly, one of the new mutant loci added to CH.1.1 (L452R) used to be a characteristic mutant locus for the Delta mutant strain. However, “the mutant locus is also present in many other subbranches of the Omicron variant strain, such as BA.5.3 and BA.5.1.3.”

According to the report, CH.1.1 has shown an increasing trend in the prevalence of new coronavirus strains in the U.S. from November 2022 to the present. in week 4 of 2023, CH.1.1 was the fifth most prevalent strain in the U.S., behind XBB.1.5, BQ.1.1, BQ.1 and XBB variants.

According to the Global Influenza Shared Database (GISAID) accession sequence, CH.1.1 was first collected and found in India on July 8, 2022. In the last 1 month, CH.1.1 and its subbranches accounted for more than 6% of the global sequence count. As of January 30, 2023, it has been found in 67 countries or regions under surveillance, mainly in the United Kingdom, Denmark, Singapore and other countries, and accounts for about 25% of the new coronavirus sequences uploaded in the United Kingdom in the last month.

For the detection of CH.1.1 in China, the CDC article describes that on November 13, 2022, CH.1.1 evolutionary branch was detected for the first time in China by genome sequencing from a sample of an imported case from Thailand (sampled on November 10, 2022) reported by Tianjin. As of January 30, 2023, a total of 24 imported cases of CH.1.1 and its subbranches were detected through surveillance. The origin of imported cases involved 15 countries or regions. No indigenous infection cases of CH.1.1 and its subbranches have been monitored.

The CDC said that enhanced pathogenicity of the CH.1.1 mutant strain has not been seen yet and still requires further attention. Generally after the emergence of a new strain, infected cases need to reach a certain size and last for a certain period of time before the pathogenicity of the new strain can be initially judged to be changed.

In this regard, Zhao Wei, director of the Center for Biosafety Research at the School of Public Health of Southern Medical University, pointed out in an interview with the People’s Daily Health Client that the CH.1.1 virus variant is one of the Omicron subvariants monitored by the WHO, “From the data, the CH.1.1 virus variant has some immune escape ability and may cause new infections, but its pathogenicity in the population pathogenicity is not significantly enhanced.”

“Although the immune escape capacity and transmission advantage of the CH.1.1 variant are further enhanced, leading to an increased risk of breakthrough infection and reinfection, high levels of neutralizing antibodies already exist in most of our population, which provide some cross-protection against CH.1.1, and CH.1.1 will not cause a large indigenous epidemic in the short term. Vulnerable populations (people over 65 years old, people with underlying diseases and unvaccinated people) and uninfected people still need to strengthen personal protection.” CDC said.

In fact, the new coronavirus has been in a constant process of mutation, and at least five major subtype strains, ba.1, ba.2, ba.3, ba.4, and ba.5, have evolved since the Omicron mutant strain was detected and continue to evolve and reorganize.

On January 19, 2022, the mutant strain xe was detected in the UK as a result of the recombination of Omicron ba.1 and ba.2. xd and xf are the result of the recombination of Delta and Omicron ba.1, and are therefore also known as “Delta Kron”. The xf is the result of the recombination of the British ba.1 and Delta, while the xd is the result of the recombination of the French ba.1 and Delta.

In addition, the variant XBB, which has attracted a lot of attention, belongs to the same subbranch of Omicron and is a recombinant variant of the variant below BA.2. The Global Influenza Shared Database (GISAID) shows that XBB.1.5 has been identified in at least 74 countries and territories as of Dec. 31, 2022, and that it has spread to 43 states in the United States.

According to the WHO’s weekly COVID-19 epidemiological update on Jan. 25, BA.5 and its progeny are still dominant globally, and the prevalence of BA.2 and its progeny spectrum is increasing. Meanwhile, WHO is closely tracking four Omicron subbranches, including BF.7, BQ.1, BA.2.75, and XBB. globally, from October 22, 2022 to January 23, 2023, 8,931 Omicron XBB.1.5 variant sequences (excluding low-coverage sequences) were reported from 54 countries, with the majority of sequences from the United States ( 75.0%).

Previously, virologist Rongshan Chang said in an interview with Interface News that the new coronavirus epidemic has produced hundreds of variants over the past three years due to the huge number of infections, in which the most adaptive variants became globally prevalent, from the early primitive strains to the Omicron strains, all of which were produced through successive evolution. Since the last year, all global epidemic strains have been generated by internal recombination of the Omicron strain, and the virus has become much more adaptable in the population.

According to Chang Rongshan, analysis of virological theory shows that virulent strains (e.g., causing host death) are difficult to persist, while relatively harmless strains get perpetuated together with the host. As the virus passes through new hosts, it has a gradual change from incompatible to compatible with the new host, so the virus has a natural characteristic of “passing down virulence”. The current epidemic strain has not yet reduced the mortality rate to one in a million, and is still a long way from a natural “live attenuated vaccine”, so there is still a need for vaccination to reduce the rate of severe illness and mortality among the “old and young” population.

On January 9, 2023, Wang Guiqiang, director of the Department of Infectious Diseases at Peking University Hospital No. 1, told a press conference on the State Council’s joint prevention and control mechanism that “the pathogenicity of the Omicron strain is reduced after infection, and the infectiousness is significantly increased, and overall, compared with the Delta strain and the original strain, its pathogenicity is significantly reduced.” The clinical manifestations of the Omicron strain are mainly fever, cough, malaise, etc. Individual patients may develop pneumonia, but the overall incidence of pneumonia is significantly reduced compared to that of the Delta strain.

As for the situation of the new coronavirus variant found in China, Chen Cao, a researcher at the Institute of Viral Diseases of the Chinese CDC, introduced at a press conference on January 30 that surveillance data showed that the current round of the epidemic in China is still mainly BA.5.2, BF.7 as the main prevalent strain, no other dominant virus strains have been monitored. During the Spring Festival holiday, the Chinese CDC received 1,421 whole genome sequences of the new coronavirus reported by the provinces nationwide, and after analysis found that they had 11 evolutionary branches, still dominated by BA.5.2, BF.7, and no new mutant strains were found to be imported.