A medic conducts a COVID-19 test on a woman as mass testing rolls out in some areas of Tai'an City, Shandong Province, March 29, 2022. (Photo: CFP)

The number of daily asymptomatic COVID-19 cases in Shanghai has been in the thousands for about a week, while the number of daily positive cases has been in the dozens.

Although asymptomatic cases do not count as confirmed cases, they still need to be quarantined. This has sparked confusion among the public.

Zhang Boli, a Chinese epidemiologist and academician at the Chinese Academy of Engineering, explained all things related to asymptomatic cases in China.

Why are asymptomatic cases surging in China?

"More infected people are asymptomatic and the rate of asymptomatic infections is rising," said Zhang. "It's a distinctive trait of the new wave of COVID-19 flare-up China."

Zhang said several factors are contributing to the dramatic surge in asymptomatic cases in the country.

Omicron, the new COVID-19 variant dominating globally, is more transmissible but less severe, compared to other variants, said Zhang. "That's why many infected people don't show symptoms at the early stage."

He warned that infected people with no symptoms can't let their guard down. "Asymptomatic infections are still transmissible and harder to be discovered. Plus, the symptoms could emerge and develop in the following day," said Zhang.

The country rolling out early screening tests among a wider population amid the COVID-19 resurgence is another reason why so many asymptomatic infections are being discovered. The test has helped detect many infected people who show no symptoms in the early stages of infection, the expert said.

"In addition, we have a high vaccination rate among the public," Zhang said. "The immune systems of the vaccinated have been boosted, so a lot of people are asymptomatic when infected."

Are asymptomatic infections dangerous? How to prevent it?

Past records show many close contacts of asymptomatic patients test positive for COVID-19, Zhang said, meaning "asymptomatic cases can cause several infections unnoticeably since they are not easily detected."

"Asymptomatic patients still carry a certain amount of virus, which is equally transmissible [as symptomatic cases]," he said. "The increase of asymptomatic cases makes it more challenging to detect all the infections, at the same time, it can spread fast if we don't contain it timely."

Zhang advised swift actions must be taken to track all infections, including asymptomatic cases, "so we could sever its local transmission and hit the goal of dynamic zero COVID-19 infection."