We don’t have enough information yet to say how protected someone might be from being infected again if they have antibodies to the virus.
https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/anti...
How long IgM and IgG antibodies remain detectable following infection is not known.
...
it remains uncertain to what degree and for how long individuals with antibodies (neutralizing or total) are protected against reinfection with SARS-CoV-2 or what concentration of antibodies may be needed to provide such protection.
https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/anti...
Sure, but it seems to have worked so far. And if having natural antibodies doesn't give long-term immunity, then will vaccine-induced antibodies? We don't know.
> "How long IgM and IgG antibodies remain detectable following infection is not known."
Having detectable antibodies is not the same thing as immunity.
Many such people will have antibodies already. As do I. I’ll get the vaccine if it becomes a requirement to travel or whatever, but I see no need for it in the short term if you’re low risk and already had Covid.