(Yicai Global) April 15 -- Wuhan has become the ninth Chinese region to start a seroepidemiological survey of asymptomatic Covid-19 patients to better understand the virus.

The city that was the epicenter for the virus began a three-day survey on 11,000 people yesterday, according to a team with the Chinese Center for Disease Control and Prevention in the city.

The survey is part of a series nationwide examining how the infection affects healthy people and asymptomatic carriers and immunity levels, the team’s leader Ding Gangqiang said, adding that it will provide a scientific basis for defining a Covid-19 prevention and control strategy.

“The survey is of great significance,” an unnamed epidemiologist added. “We will rely on it not just to know the Covid-19 infection rate but also the proportion of asymptomatic infections and their impact on controlling the virus. We also need to find out the degree of herd immunity, which can only arise when at least 60 percent to 80 percent of a population has become immune to an infectious disease.”

It will include all family members who stayed in one of 100 communities in the city for at least 14 days between January and last month, with testees undergoing a throat swab nucleic acid test and blood test for immunoglobulins IgC and IgM.

Jiangsu and Liaoning provinces announced they would start similar surveys on April 12 and April 13.

Editors: Zhang Yushuo, James Boynton