The rising number of asymptomatic cases in the latest COVID-19 outbreak in China is due to the low pathogenicity of the Omicron variant, as well as timely screening, early detection of infections and wide vaccination coverage, a top Chinese expert said on Monday.

Zhang Boli, an academician at the Chinese Academy of Engineering, said in an interview with Science and Technology Daily while the variants of the novel coronavirus are more contagious, their severity is relatively weak.

"The clinical manifestation of weakened virulence of viruses is the patients' symptoms are milder, and many patients do not show symptoms for a short time after being infected," Zhang said.

He cautioned that, although analysis in other countries showed the Omicron variant has a decreased fatality rate compared with the Delta variant, it is still highly contagious.

"Patients with no symptoms could show symptoms later, especially vulnerable groups such as senior adults, people with underlying health conditions, as well as those with obesity and heavy smokers. They are at risk of developing into cases with symptoms and taking a sharp turn for the worse," he said.

For generally asymptomatic carriers, the key is to put them under medical observation in isolation. Taking traditional Chinese medicine is encouraged, first to prevent them from showing symptoms and developing into moderate cases; second to help their nucleic acid tests turn negative as soon as possible.

According to Zhang, timely nucleic acid testing after a virus outbreak, along with widespread vaccination in the country also explained why most cases being found were asymptomatic.

In the latest COVID-19 outbreak caused mainly by the Omicron variant, the Chinese mainland on Monday reported a new daily record of 5,658 locally transmitted asymptomatic cases, among which 4,381 were from Shanghai. The current strategy adopted by the city is aimed at breaking transmission chains by rotating grid testing and lockdowns of areas with higher exposure to the virus, according to Zhang Wenhong, head of the infectious disease department at Huashan Hospital in Shanghai.

The hiking number of asymptomatic cases bring challenges to virus prevention and control in the country. "Rapid and strict work tracing the source of the outbreak must be carried out. Only by finding all asymptomatic carriers in the shortest time and completely blocking community transmission can achieve zero-COVID in the whole society," Zhang Boli said.