https://www.dailywire.com/news/early-antibody-testing-in-chicago-30-50-of-those-tested-for-covid-19-already-have-antibodies-report-says

Early Antibody Testing In Chicago: 30-50% Of Those Tested For COVID-19 Already Have Antibodies, Report Says

By  Amanda PrestigiacomoDailyWire.com

Abs COVID-19 structure - 3d rendered image structure view on black background. Viral Infection concept. MERS-CoV, SARS-CoV, ТОРС, 2019-nCoV, Wuhan Coronavirus. Design element. RNA. High resolution.
At a hospital in Chicago, a non-randomized sample found that 30-50% of patients tested for COVID-19 have antibodies in their system, suggesting they already had the virus and have potential immunity. (See link for article)
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**Comment**
Again, I feel I had this back in January – as did my entire family. I’ve spoke with many friends and they say the same.
Excerpt:
Professor Knut Wittkowski, for twenty years head of The Rockefeller University’s Department of Biostatistics, Epidemiology, and Research Design, says that social distancing and lockdown is the absolutely worst way to deal with an airborne respiratory virus.
Further, he offers data to show that China and South Korea had already reached their peak number of cases when they instituted their containment measures. In other words, nature had already achieved, or nearly achieved, herd immunity.
Our current course, he warns, will only prolong the crisis and likely guarantee a second wave of infections in the Fall.
Herd immunity, remember that? It’s the argument used repeatedly for pushing vaccines, yet when it comes to a wild virus and the body’s innate ability to create antibodies to it, all the vaccine proponents go silent on herd immunity and only see a vaccine.  
Excerpt:  
An elderly man critically ill from the coronavirus is among the first few patients in Milwaukee to receive a plasma transfusion in hopes that the antibodies from someone who has recovered from COVID-19 will help his body fight the virus.
The only problem is the lack of plasma donors.
In order to be eligible to donate patients have to be symptom free for 28 days, or for at least 14 days with a verified negative test. 
Recovered patients interested in donating plasma can apply online.