Dockers wear protective clothing at a port in Yantai, East China's Shandong Province, on April 25, 2022. Photo: VCG

Cases of COVID-19 infection by an evolved sublineage of Omicron's BA.2 mutation, Omicron BA.2.3, were reported on Monday in Yantai, East China's Shandong Province, the first time the strain has been detected in the Chinese mainland.

Genetic sequencing shows that 16 cases reported in the port city belong to the same transmission chain, caused by this evolved variant, the city's health authorities said at a news conference on Monday. The new variant has proven to be more contagious with a shorter incubation period.

Yantai reported 36 confirmed COVID-19 cases, along with 34 silent carriers on Sunday. The city has recorded an increasing number of cases in recent days. It has vowed to quickly stamp out all transmissions, and to eliminate viral infections within communities as soon as possible.

Meanwhile, immunologists told the Global Times that the emergence of this new strain in China is not expected to make a major difference to the country's epidemic fight. There is a high possibility that this strain was imported from outside of the mainland.

"However, since its mutation is not a significant change from its predecessor strain, it is not expected to have an impact on the overall epidemic situation and prevention measures in China," Zhuang Shilihe, a Guangzhou-based immunologist, told the Global Times on Monday. 

Current data has shown no evidence of significant changes in BA.2.3's infectiousness and immune escape capacity, but a growing number of cases have been reported in some countries. 

The strain's relative growth advantage is 17 percent globally, implying that it is causing more infections worldwide.

According to the results of the global sequencing of the COVID-19 gene, Omicron BA.2.3 has now been detected in 49,000 sequences worldwide, accounting for 6.2 percent of all strains, Zhuang cited data as saying. Most of the previous cases were found in Europe.

Zhuang pointed out that the BA.2.3 strain found in Yantai could hardly have emerged as a local mutation, but must have been imported from outside the Chinese mainland.

Although mutations in the virus are random, they tend to occur more often in areas with large numbers of cases and in populations with immune deficiencies, Zhuang explained, noting that the situation in China doesn't match up.

"Yantai has never had a large number of cases," Zhuang said, "and from previous experience, China has never been the origin site of mutated strains either."

For Omicron and its sublineages, current vaccines have still proven effective in preventing severe illness and reducing deaths, Zhuang told the Global Times. This is not expected to change much as the BA.2.3 variant does not have significant mutations from its predecessors.

"But experience has shown that if dynamic clearance for COVID-19 infections is to be maintained, then timely and effective prevention and control needs to be maintained in addition to the vaccine," he said, noting that the emergence of BA.2.3 in China is not expected to have a significant impact on the epidemic prevention situation.

Yantai is an important port on the Bohai Sea in China, and is across the sea from Japan and South Korea, with which it has frequent cargo traffic.