https://arstechnica.com/science/2020/06/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.
