I recommend reading this blog post [1] about the unknowns of immunity. Antibodies are only part of the immunity picture, as this tweetstorm [2] concisely explains.

[1] https://blogs.sciencemag.org/pipeline/archives/2020/07/07/mo...

[2] https://twitter.com/EricTopol/status/1278400526716211200?s=1...