How many people have been infected with SARS-CoV-2 without being detected?

As everyone knows, that is the most important unanswered question in this sordid pandemic to date. Infection with SARS-CoV-2 is often mild or even completely asymptomatic, and with the tremendous gaps in testing in the US it is self-apparent that many cases have gone undetected, both by the authorities and by patients themselves. But knowing this figure is crucial for two major reasons: first, anyone who has been infected with SARS-CoV-2 (and survived) is now presumably immune and can re-enter society with few worries. But second, the larger the percentage of undetected cases turns out to be, the less menacing the virus becomes. Yet despite well over 5,000 scientific papers on the novel coronavirus in the past four months, there has not been a single reliable “antibody study” to date. Until today.