It's very, very unusual that someone can't be given any of the covid vaccines (in general, even if you're allergic to the ingredients in one, another will be suitable). Immunocompromised people are generally vaccinated (they're one of the first groups that most countries did) but it's questionable how effective the vaccine is in them; it is, at best, likely less effective than in the general population. And, certainly, in heavily vaccinated countries, ICUs are largely a mix of the few unvaccinated, and vaccinated people who are either immunocompromised or have very severe health problems. Antivirals have an obvious role to play, there.