Some studies done on the amount of antibody in people who were infected with COVID and recovered.
The most disturbing part is that people do NOT necessarily develop strong immunity to further infection: it varies widely from person to person.
This makes it much more difficult to get herd immunity and guaranteed safety to open up.
Antibody testing suggests immune response post-COVID is very variable
"For now, what do we conclude from all of this? The first is that, to get a more accurate picture of who has actually experienced a SARS-CoV-2 infection, we're going to want to rely on high-throughput assays. Right now, the smaller personal kits may be helpful for people who are interested in getting a rough picture of their own medical history, but the results aren't up to the quality we'd want for understanding the public's exposure.
The second thing is that SARS-CoV-2 infection isn't necessarily producing a robust immunity. We don't really know what levels of neutralizing antibodies are actually protective, but
it's clear that a lot of people don't produce many of them after an infection. Which means any plans for generating herd immunity by allowing a controlled level of infection have to be viewed with extreme skepticism at this point. And vaccine developers will need to ensure that the injections produce a consistently high-level response that includes neutralizing antibodies."