A medical staff member collects samples for nucleic acid testing in Yangpu District, Shanghai, March 18, 2022. (Photo: CFP)

Timely virus screening and the large amount of vaccine doses administered in China may be responsible for a large number asymptomatic cases amid the new epidemic outbreak, Professor Zhang Boli of the Chinese Academy of Engineering told the Science and Technology Daily on Monday.

Noting the new sharp increase in asymptomatic cases, Zhang pointed out the rise is related to the Omicron variant. According to research, when viruses accumulate many mutations they lose some virulence. Scientists around the world found that the mortality rate of the Omicron variant has decreased, indicating that the pathogenicity of Omicron was not as strong as other variants, Zhang said.

Mass virus screenings also give us early detection, as many patients do not show symptoms in the early stage of infection, Zhang noted. Most of asymptomatic cases were detected by citywide nucleic acid testing before patients went to the hospital amid this round of the epidemic.

Another important reason is that people have been vaccinated on a large scale, Zhang explained. Booster vaccinations can effectively reduce the risk of breakthrough infections caused by the Omicron variant and the immunity of the population is generally enhanced.

Asymptomatic infected patients have no clinical symptoms but are still infectious, Zhang stressed. Mass nucleic acid testing and effective quarantine measures are still needed to further contain the spread of the virus.

(Compiled by Wang Zi)