Race against variants Illustration: Liu Rui/GT

China reported the first case of a COVID-19 infection caused by the "more contagious" Omicron BA.4 variant, which was imported, according to an epidemiological survey by the Chinese Center for Disease Control and Prevention.

On May 4, a case of Omicron BA.4 infection was confirmed in China, the first reported in the country. The patient arrived in Guangzhou, South China's Guangdong Province from the Netherlands on April 29 and was admitted to an isolation hotel. The next day, she tested positive for novel coronavirus.

The 20-year-old patient had been fully vaccinated and complied with the 14-day pre-departure requirements prior to the flight.

Public information showed that Omicron BA.4 is the latest variant to cause an outbreak in South Africa and is rapidly replacing BA.2. Studies have shown that this subvariant exhibits stronger immune escape in recipients of three doses of the vaccine, and that it may escape antibodies elicited by previous Omicron infection. 

"There are some studies that suggest BA.4 is about 10 percent more infectious than BA.2, and its R0 may have exceeded 10," Zhuang Shilihe, a Guangzhou-based immunologist, told the Global Times. "But as most people have received at least two doses of COVID-19 vaccine, more data are needed to assess its exact transmission capacity. There is also no evidence yet of a significant change in its pathogenic capacity."

Cases involving the BA.4 subvariant have been reported in at least 20 countries and regions, with a total of more than 1,300 cases.

WHO's technical lead on COVID-19 Maria Van Kerkhove said that the BA.4 variant appears to be more contagious. However, the WHO epidemiologists have not seen any change in epidemiology or severity compared with former variants, according to a May 11 news release. 

Other infections caused by new Omicron mutant strains have also been reported in China recently.

On April 27, China reported the first infection caused by Omicron BA.2.12.1. The infected individual arrived in Guangzhou from Kenya on April 23 and was transferred to an isolation hotel. Four days later, he tested positive and was transferred to a hospital for treatment. The infected man had been fully vaccinated.

Multiple studies have shown that BA.2.12.1 spreads about 23-27 percent faster than BA.2, and that this mutant strain is one of the main causes of the current rebound in many parts of the US. At least 17 countries have reported cases of the BA2.12.1 subvariant, according to media reports.

Recent epidemiological surveys have shown that the strain that recently triggered a larger infection in Guang'an, South China's Sichuan Province, was Omicron BA.2.2. More than 1,000 people were infected in this wave of the outbreak.

While new Omicron subvariants have been found in China, experts said the public does not need to worry too much, as China's strict anti-epidemic measures and early detection can effectively control the spread.  

As more new variants emerge, China, along with the international community, can focus on accelerating the development of drugs and next-generation vaccines, and continue to improve non-pharmaceutical intervention strategies based on the characteristics of the prevalent strains, Zhuang said.