Research seems to indicate that the antiviral affects linger for some time, but the drug hasn't been out there long enough to determine just how long that would be.
“This shot will spring you out of the ICU, if that’s where you are.”
the EUA of the Regeneron monoclonal antibodies prohibits their use for anyone who is hospitalized ...
https://www.google.com/search?q=regeneron+eua+hospitalized
“Seriously effective, but it’s just an antiviral, not a vaccine.”
You aren’t using ‘antiviral’ properly. An antiviral is Tamiflu. Remdesivir is another. Regeneron is a monoclonal antibody, as you see it invariably described.