Over half of the people infected with virus were not showing symptoms

The Chinese mainland reported more than 800 locally transmitted COVID-19 infections for Wednesday, nearly double the previous day's count, with experts saying the novel coronavirus' rampage in neighboring countries and regions and the high ratio of asymptomatic cases had contributed to the surge.

For the fourth day in a row, asymptomatic cases－people who are infected with the virus but show no symptoms－accounted for more than half of total new infections.

As China sticks to its goal of eliminating local outbreaks as soon as they occur, experts have called for the upgrading of the country's mass immunization strategies and accelerating screening of high-risk groups.

"Imported cases and domestic infections will likely continue to exist for some time, and our goal is to keep the virus' spread at a very low level … preventing large-scale virus flare-ups is the bottom line of our virus control work," Zhang Wenhong, head of the infectious disease department at Fudan University's Huashan Hospital, said this week.

The Chinese mainland registered 402 locally transmitted confirmed cases in 16 provincial-level regions on Wednesday, with a number of outbreaks confirmed to be of the Omicron variant, according to the National Health Commission and local health authorities.

Meanwhile, 435 asymptomatic infections were detected on Wednesday, with the majority concentrated in Jilin and Shandong provinces, as well as Shanghai.

Jilin, in Northeast China, reported the highest daily number of 165 confirmed cases for Wednesday, followed by Shandong and Gansu province, which each reported 66.

Zhang Lifeng, Party chief of Jilin Agricultural Science and Technology University, was removed from his post on Thursday after a large number of cases broke out on the campus.

Wang Guangfa, head of Peking University First Hospital's department of respiratory and critical care medicine, said that the scattered infection clusters are mainly a result of difficulties in identifying the high number of asymptomatic cases, as well as increasing pressure from overseas.

"The dominant strain at present is Omicron, which leads to mild and less typical symptoms," he said. "Plus, with a large number of people having received COVID-19 vaccines, some cases do not have fever or any respiratory symptoms. Often we are unable to detect the virus until it has transmitted for some time."

Omicron's ability to transmit in a rapid and stealthy manner has enabled it to replace the Delta strain as the most common one, fueling a new wave of global infections that peaked in January in some countries.

Even though the tally of infections worldwide has dropped by two-thirds compared with the peak in late January, the pressure on China is nonetheless high, experts said.

According to data from the World Health Organization, a number of countries and regions registering the highest number of infections in the past week neighbor China, including South Korea, Vietnam, Russia and Japan. Hong Kong is also battling its fifth wave of the pandemic.

Zhang said Shanghai reported more than 1,240 imported infections in January and February, equal to about 80 percent of the total number of imported cases registered last year.

"In terms of disease control policies in the future, the formulation of vaccination strategies is critical," he said. "As long as we maintain good momentum in emphasizing vaccination, coupled with enforcing adequate triage systems at hospitals, it is hopeful for the world to exit the pandemic."

By the end of February, more than 87 percent of the Chinese population was fully vaccinated, according to authorities.

Zhang said that none of the 2,200-plus infections in the past six months in Shanghai－with about 94 percent of them vaccinated－has developed into critical cases or died of the disease, reaffirming the strong link between immunization and severity of condition.

He added that the rate of severe cases is even lower among people who have been given a booster shot.

"As China is widely promoting its booster campaign, upgrading its vaccination strategy and pushing research into antiviral drugs, our capability in coping with the virus will continue to improve," he said.

Lu Jiahai, a professor at Sun Yat-Sen University's School of Public Health, also suggested advancing research and deployment of vaccines tailored to new strains.

It is also important to improve the sensitivity of nucleic acid tests and speed up mass testing campaigns, he added.