No local infections linked to Omicron variant CH.1.1 have been found on the Chinese mainland so far and the variant is unlikely to lead to large-scale domestic transmission in the short term, the Chinese Center for Disease Control and Prevention (Chinese CDC) said on late Tuesday night in response to the public concern over the new variant that has been detected in over 60 countries.
The first Omicron CH.1.1 case in the Chinese mainland was reported in North China’s Tianjin on November 13, 2022. It was detected through genome sequencing of a sample collected on November 10, 2022 from an imported case from Thailand, the Chinese CDC said on its official WeChat account.
As of January 30, 2023, a total of 24 imported cases of CH.1.1 variant and its subvariants have been detected throughout the mainland. The sources of these imported cases involve 15 overseas countries and regions. So far, no local infections of CH.1.1 and its subvariants have been detected on the Chinese mainland, according to the Chinese CDC.
Despite that the immune escape capacity and transmission advantage of CH.1.1 variant have further enhanced and can lead to an increasing risk of breakthrough infection and reinfection, the variant will not cause large-scale domestic transmission in the short term since the majority of China’s population has already obtained high levels of neutralizing antibodies, which provide certain cross-protection effect against CH.1.1, the Chinese CDC noted.
However, the vulnerable groups including those aged 65 or above, those who have underlying diseases, and those who have not been vaccinated, as well as those who have not been infected of COVID-19, still need to strengthen personal protection, the Chinese CDC said, reminding the public to persist in personal protection and good hygiene habits.
According to the Chinese CDC, CH.1.1 is the sixth-generation sub-lineage of Omicron BA.2.75. The latest researches have shown that the immune escape capacity of CH.1.1 has strengthened due to the increase of multiple substitutions, among which, the L452R substitution was the characteristic substitution of Delta variant. It is also noteworthy that the L452R substitution also exists in many other Omicron variants and subvariants such as BA.5.3 and BA.5.1.3.
Since November of 2022, the proportion of CH.1.1 in the prevailing mutant strains in the US has been rising. As of the fourth week of 2023, the proportion of CH.1.1 in the prevailing mutant strains in the US has ranked the fifth, following XBB.1.5, BQ.1.1, BQ.1 and XBB variants.
The Chinese CDC said that no enhancement of the virulence of CH.1.1 variant has been observed at present, but further monitoring is still needed. Usually, after the emergence of a new variant, the number of infections needs to reach a certain scale and continues for a period of time to determine whether the virulence of the new variant has changed.
Statistics from the Global Initiative on Sharing Avian Influenza Data (GISAID) show that the CH.1.1 was found for the first time in India on July 8, 2022. Over the past month, CH.1.1 variant and its sub-lineages have accounted for over 6 percent in the global lineages recorded.
As of January 30, 2023, the CH.1.1 variant has been detected in 67 countries or regions and has become the most prevalent variant in countries including UK, Denmark and Singapore. CH.1.1 variant has accounted for about 25 percent of the COVID-19 sequences uploaded in the UK over the last month.