We have found imported cases of CH.1.1 mutant strain in China, and you need to know about it.

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According to a news release from the Chinese Center for Disease Control and Prevention (CDC) on the evening of January 31, the Omicron mutant strain CH.1.1 has been detected in 67 countries or regions, and the CDC said that as of January 30, 2023, no indigenous cases of CH.1.1 and its subbranches have been monitored in China. High levels of neutralizing antibodies already exist in most of the population in China, and there is some cross-protection against CH.1.1. CH.1.1 will not cause a large indigenous epidemic in the short term.

1、What is the Omicron variant CH.1.1?

CH.1.1 belongs to the sixth generation subbranch of the Omicron variant BA.2.75. Recent studies have shown that the immune escape ability of CH.1.1 has been increased by the addition of several mutation sites. Meanwhile, one of the added mutant sites (L452R) used to be a characteristic mutation site of the Delta mutant strain. However, it is noteworthy that this mutant locus is also present in many other subbranches of the Omicron variant strain, such as BA.5.3 and BA.5.1.3.

From November 2022 to the present, CH.1.1 has shown an increasing trend in the proportion of new coronavirus prevalent strains in the U.S. In week 4 of 2023, CH.1.1 was the fifth most prevalent strain in the U.S., after XBB.1.5, BQ.1.1, BQ.1 and XBB variants.

Will CH.1.1 be more pathogenic?

At present, no enhanced pathogenicity of CH.1.1 mutant strains has been observed, but further attention is still needed. Generally, after the emergence of a new strain, the infected cases need to reach a certain scale and last for a certain period of time before the pathogenicity of the new strain can be initially judged to be changed.

CH.1.1 Global epidemiological characteristics

According to the sequence included in the GISAID database, 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 prevalent in the UK, Denmark, Singapore, etc. It accounts for about 25% of the new coronavirus sequences uploaded in the UK in the last month.

CH.1.1 Detection in China

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 reported by Tianjin (sampled on November 10, 2022). 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 were monitored.

Can CH.1.1 cause a second round of infection?

Although the immune escape ability and transmission advantage of the CH.1.1 mutant strain have further increased, leading to an increased risk of breakthrough infection and reinfection, high levels of neutralizing antibodies already exist in most of the population in China, and there is some cross-protection against CH.1.1. CH.1.1 will not cause a large-scale local epidemic in the short term. Vulnerable groups (elderly people over 65 years old, patients with underlying diseases and unvaccinated people) and uninfected people still need to strengthen personal protection.

6、How to face CH.1.1?

Insist on good personal protection, maintain good hygiene practices, and do not believe unconfirmed internet reports.