Having antibodies does not guarantee immunity.
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.
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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...