A few things to remember. Antibodies dont stay expressed for high amounts for long levels of time forever after infection - imagine if your body was 100% agains

A few things to remember. Antibodies dont stay expressed for high amounts for long levels of time forever after infection - imagine if your body was 100% against every infection you ever encountered forever? The important factor is that your body remembers what antibody to make and then makes it when the next infection happens. Depending on the sensitivity of the test you might not see a response. And a second important point - antibody mediated immunity is just one form of immunity. Cell mediated immunity definitely plays a role against coronavirus [1] and this doesnt test for the presence of reactive T cells etc. We arent getting a complete picture. Also, if 5% of people have been infected, and all of them make antibodies, then that means herd immunity is still reachable. We dont have the data we need to figure out the complete fraction. And of course, a vaccine will help us artificially boost our way to herd immunity. [1] https://www.sciencemag.org/news/2020/05/t-cells-found-covid-19-patients-bode-well-long-term-immunity https://www.sciencemag.org/news/2020/05/t-cells-found-covid-...