SHANGHAI (Reuters) – China has launched an epidemiological survey in nine regions in an effort to determine the full scale of asymptomatic infections and overall immunity levels, the official China Daily newspaper reported on Wednesday.

Amid rising concerns that the ending of lockdowns would release thousands of asymptomatic but infectious people back into circulation, China’s central government coronavirus task force said at the end of March that it would conduct widespread serological surveys in key areas.

The epidemiological survey was launched on Tuesday in the Jiangxia district of Wuhan, where the COVID-19 pandemic originated. Blood samples and throat swabs were taken from randomly selected residents for testing, China Daily said.

“The goal is to understand the antibody levels in communities and provide scientific evidence for future adjustments in strategies to control the epidemic,” it quoted Ding Gangqiang, a Chinese disease control official, as saying.

The survey will test 11,000 citizens in Wuhan, a thousandth of its total population. The cities of Beijing, Shanghai, and Chongqing, as well as the provinces of Liaoning, Jiangsu, Zhejiang, Guangdong and Sichuan, will also be surveyed.

China has reported a total of 82,295 confirmed coronavirus cases by the end of Tuesday, with 3,342 deaths. Globally, more than 1.9 million have been infected and over 120,000 have died.

(Reporting by David Stanway; Editing by Himani Sarkar)