Its been suspected for quite a while now that covid can mutate fast enough so the concept of immunity is null. Whats not currently known is how much past infection helps prevent reinfection and how long to expect the antibodies you do produce to stick around. There have already been suspected cases of reinfection. People have tested positive and been hospitalized on separate occasions months apart after testing positive for covid19 both times. It can't definitively be claimed yet though, as its possible that the first infection of covid was weakened by the patients immune system, but then regained strength and knocked them down again rather than reinfection.