No indigenous cases of CH.1.1 and its subbranches have been monitored in China. Those with underlying diseases and unvaccinated people still need to strengthen personal protection

Read Time:2 Minute, 9 Second

The CDC recently released information about the CH.1.1 variant strain, noting that no indigenous cases of CH.1.1 and its subbranches have been monitored in China.

CH.1.1 belongs to the sixth generation subbranch of the Omicron mutant strain BA.2.75. The latest study showed that the immune escape ability of CH.1.1 was increased due to the addition of several mutant loci. 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. At present, no enhanced pathogenicity of CH.1.1 mutant strains has been observed, and 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 we can initially determine whether the pathogenicity of the new strain has changed. As of January 30, 2023, CH.1.1 has been detected in 67 countries or regions under surveillance, with prevalence mainly in the United Kingdom, Denmark, and Singapore.

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. 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 describes that although the immune escape capacity and transmission advantage of the CH.1.1 mutant strain has 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, which provide some cross-protection against CH.1.1 and will not cause a large local epidemic in the short term. However, here is a reminder that vulnerable populations, such as those over 65 years old, patients with underlying diseases and unvaccinated persons, as well as uninfected people still need to strengthen personal protection.