My thoughts on this is that MABs are pretty harmless. If you have an allergic reaction, that is treatable and would occur before you leave the infusion center. More of an itchy rash reaction than epi-pen time.
But they are pretty damned expensive for three months of immunity: The government is paying about $3000 per treatment, versus $30 per vaccine. And the vaccine will give you much longer lasting immunity. Then there is the little problem of efficacy: A recent paper reported the best MABs keep about 50% more people from getting hospitalized. mRNA vaccines keep around 95% of people from getting hospitalized!
When your three months is up, your health care provider is going to tell you get vaccinated before you get reinfected. MABs do NOT provide any long-lasting immunity like a vaccine does. Of course, neither does mulnupiravir. Five days after a treatment course, you could get reinfected because you have no antibodies or activated T-cells.
It's idiotic to waste MABs on people who could get vaccinated. We should save them for people with medical conditions that prevent them from developing antibodies.
We're flying electric helicopters on Mars yet you can't turn on your clothes dryer in Texas. That's because scientists are in charge of Mars, and Republicans are in charge of Texas.