That is an interesting question, presently monoclonal antibodies are used as an early intervention against a known Covid infection, and must be given early after the diagnosis. They have been tested in high-risk populations with a KNOWN exposure, like in a nursing home, and showed effectiveness, but it was before widely available vaccine.

I am thinking the problem would be access and timing to use them prophylactically. Currently, the antibodies require cold storage and IV infusion, so are not suitable for self-administration.
Sue