There is some evidence that a person that is infected by this corona virus has some level of resistance to illness that lasts for a variable amount of time, but can still harbor and spread the virus.
Sounds just like a vaccinated person. The resistance comes from antibodies. Are the antibodies different? Can you take a blood test from a person and differentiate between antibodies created as a result of having been infected versus antibodies created as a result of having been vaccinated?