Are there countries who conduct serologic tests? PCR tests (widely used?) wouldn't catch people who got the infection, developed antibodies with no or mild symptoms, but didn't transmit the virus around at the moment test is taken.

From the article about Covid-19 serologic test development:

> The serologic tests, which are different from the ones used to diagnose active infection, would allow researchers to test the blood of people who were not confirmed cases of Covid-19 in communities where the virus spread. They would be designed to look for signs that people have mounted an immune response after being exposed to the virus.

https://www.statnews.com/2020/03/11/cdc-developing-serologic...