Here is evidence that the coronavirus is not another black death, dangerous to certain sectors of the population, but still so widespread that many people have antibodies to it and did not know until randomly tested:
  https://www.nytimes.com/2020/04/21/health/coronavirus-antibodies-california.html
“Two new studies using antibody tests to assess how many people have been infected with the coronavirus have turned up numbers higher than some experts had expected. Both studies were performed in California: one among residents of Santa Clara County, south of San Francisco, and the other among residents of Los Angeles County. In both cases, the estimates of the number of people infected in those counties were far higher than the number of confirmed cases. The studies, conducted by public health officials and scientists at Stanford University and the University of Southern California, have earned the ire of critics who questioned both the recruitment methods and the analyses. In the Santa Clara County study, researchers tested 3,330 volunteers for antibodies indicating exposure to the virus. Roughly 1.5 percent were positive. After adjustments intended to account for differences between the sample and the population of the county as a whole, the researchers estimated that the prevalence of antibodies was between 2.5 percent and a bit more than 4 percent. The county’s population is 1.9 million. That means that 48,000 to 81,000 people were infected with the coronavirus in Santa Clara County by early April, the investigators concluded. In Los Angeles County, researchers conducted tests at drive-through sites and at participants’ homes and estimated that 2.8 percent to 5.6 percent of the county’s adult population carried antibodies to the coronavirus. There are 10.4 million people in Los Angeles County. If accurate, that would mean that 220,000 to 442,000 residents had been exposed. By comparison, only 8,000 cases had been confirmed in the county by early April, when the testing was done. While finding volunteers was not difficult, it’s not clear how representative they were of the populations at large.
                    