Russia’s capital is launching a large coronavirus screening program starting May 15th, the city’s mayor Sergey Sobyanin announced in a blog post.

Sobyanin said the city currently performs 40,000 coronavirus tests a day, but in order to establish the real infection rate and determine when to lift quarantine restrictions, the authorities plan to test the population for antibodies.

“The Moscow government has installed automatic blood analyzers and by the end of May the total capacity of this test system will exceed 200 thousand tests per day,” the mayor wrote. “This allows us to launch mass and free screening program on May 15th.”

A random selection of 70,000 Moscow residents will get invites via email or text every few days to get an antibody test done in one of the thirty clinics across the city, authorities said.

Testing will be carried out using enzyme immunoassay method, that detects IgM antibodies, a marker of coronavirus infection, and immunoglobulin G, a marker of immunity to the infection.

According to Sobyanin, weekly data will be published online and will be used to make “executive decisions” as to whether to ease or tighten restrictions in a city which has been under quarantine for two months.

Moscow is Russia’s worst-hit city with over 130,000 cases, although Sobyanin has said the total number of people infected is likely higher, based on previous screening studies.

“Premature removal of restrictions carries a real risk of a second pandemic,” Sobyanin said in his statement Thursday. “Unjustified delays will also hit people in the strongest way.”

On Wednesday, Moscow’s health department hit back at media reports that cast doubt on the city’s low mortality rates, with just 1,290 fatalities recorded. Health officials said the released data was “absolutely open,” but acknowledged that only deaths that were found through postmortem autopsy to have been caused directly by coronavirus complications were counted.