From July 2 to 5, the city reported 11 confirmed and 18 asymptomatic domestic cases. According to the city's center for disease prevention and control on July 5, gene sequencing showed that the case cluster was caused by the BA.5.2 subvariant.

In addition to Xi'an, the BA.5 variant had also been identified in six other cities including Beijing and Shanghai as of July 13. From July 4 to 6, Beijing reported 12 domestic cases. According to Pang Xinghuo, Deputy Director of the Beijing Center for Disease Prevention and Control, at a press conference on July 6, gene sequencing of the first three locally transmitted cases in the latest infection cluster showed that they were all caused by the BA.5.2 subvariant. "Contact tracing and gene sequencing results indicate the latest infection cluster is not on the same transmission chain as the previous local cases or imported cases. We preliminarily identified it as a local cluster linked to imported cases," Pang said.

On July 10, the Shanghai Health Commission said a COVID-19 infection registered in Pudong New Area on July 8 was found to be caused by BA.5.2.1.

New challenges 

It's not surprising that BA.5 has come to China, as it has become the dominant virus strain globally.

According to the World Health Organization (WHO), more than 4.1 million coronavirus cases were reported globally from June 20 to 26, increasing by 18 percent from the previous week. The new Omicron variants BA.4 and BA.5 are the main culprits for the worsening situation.

The BA.4 and BA.5 strains were first found in South Africa in January and February, respectively, and BA.4 and BA.5 became the main variants in the country in May.

China first found BA.4 and BA.5 from imported cases in May and recently the number of imported cases infected with BA.4 and BA.5 has been increasing.

"Initial research results show that BA.4 and BA.5 have stronger transmission and immune evading abilities, which has posed more difficulties for prevention and control," Wang Wenling, a researcher at the National Institute for Viral Disease Control and Prevention, under the Chinese Center for Disease Control and Prevention (China CDC), said at a press conference on June 28.

"BA.4 and BA.5 are variants of Omicron but they have many differences from the original Omicron because they have adopted some characteristics of the Delta variant," Liu Shanlu, a virologist from the Ohio State University, told China News Service.

"BA.4 and BA.5, having evolved from BA.2 which already has better transmission abilities than the original Omicron strain, have even higher transmissibility," Liu said.

Although BA.4 and BA.5 have only six mutations in their spike protein compared with BA.2, one mutation is crucial, which has also appeared in the Delta strain. Kei Sato, a virologist with the University of Tokyo, said this mutation may have caused the virus to attack cells more easily and to have better replication abilities.

According to a paper published in science journal Nature on June 17 by researchers from Peking University and the Chinese Academy of Sciences (CAS), Omicron variants BA.2.12.1, BA.4 and BA.5 are showing stronger immune evading abilities and are able to neutralize antibodies in the blood serum of patients who have recovered from BA.1 infections.

However, according to WHO and the European Center for Disease Prevention and Control, there is no evidence to prove that the new variants will lead to more serious illnesses than previous ones.

Liu said it remains to be seen whether the new variants will cause more serious symptoms, since large-scale clinical data often come several weeks or even one to two months behind virological studies. "Therefore, we should continue to stay vigilant," he said.

In terms of the effectiveness of current vaccines against the new variants, research shows that current vaccines are less effective in stopping transmission of the new variants than previous Omicron variants. Even the antibodies of those who have hybrid immunity, meaning those who have both recovered from infections and been vaccinated, are not always able to neutralize BA.4 and BA.5.

According to an article written by a team led by Gao Fu, an academician with the Institute of Microbiology of the CAS, which was published by the New England Journal of Medicine online on July 6, the most commonly used vaccines in China are much less effective against BA.4 and BA.5.

The article suggests developing new boosters to cope with the new variants and more possible variants to come.

However, Liu pointed out that BA.4 and BA.5 are not a fundamental departure from the original Omicron strain. He said vaccination is still crucial because scientists agree that the current vaccines haven't completely lost efficacy to the new variants and can still reduce the rates of serious cases, hospitalization and death.

Jin Dongyan, a virologist at the University of Hong Kong, told China News Service that people should receive three doses of the inactivated vaccine as a basic level of protection. Moreover, receiving a fourth vaccine shot targeting Omicron would be even more effective in preventing infections.

Wei Sheng, a professor with Tongji Medical College at Huazhong University of Science and Technology, said the dynamic zero-COVID-19 policy remains effective at swiftly stamping out new outbreaks. He added that regular nucleic acid testing, swift contact tracing and lockdowns still remain the key to preventing large-scale outbreaks in large cities.

Wang said China CDC will closely watch the development of the pandemic in other countries and keep up with the global research of new virus strains to make timely evaluation of the situation and carry out prevention and control of new Omicron variants in a scientific and targeted manner.

The coronavirus hasn't stopped its mutations and BA.5 will not be the last variant. Virus screening, vaccine updating and public health policy adjustments are all necessary to combat the virus, Wang added.

Pandemic control in counties 

In addition to the new variants, an outbreak in Sixian, a county in Anhui Province, has caught nationwide attention recently. Beginning on June 26, over 1,000 cases have been reported in the county and the virus has spread to other counties in Anhui as well as cities in neighboring Jiangsu Province.

Jin said on July 5 that the virus had been spreading for several weeks and there would be more new cases.

The outbreak has exposed the problem of pandemic prevention and control in counties. Compared with large cities, counties lag behind in nucleic acid testing and contact tracing capabilities.

Jin said counties shouldn't copy large cities' pandemic prevention measures since the former lack the ability to carry out regular massive nucleic acid testing. Counties like Sixian should watch for new cases in surrounding areas and carry out antigen tests for COVID-19 on people at high risk of infection, including medical workers, seniors and taxi drivers so as to detect cases early and curb outbreaks before they take hold.

(Print Edition Title: Containing a New Threat) 

Copyedited by G.P. Wilson 

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