I wonder if NYC hotels can do this but a lot newer HVAC system allow changing the percentage of outside air. Its advantageous for varies reasons (energy consumption, etc) to use partial recycle air but I wouldn't be surprised if certain builds have 100% outside air capabilities.
Pretty sure we're not going to find perfect solutions, only usable ones.
Perhaps filters can be jury-rigged on the vents. Maybe you only staff them with people who've already survived. Maybe you turn off the HVAC and open up the windows. Maybe it's the last resort option.
I don't think there is any evidence that recyling air has any use here given that these wards would be filled with already sick patients and healthcare professionals.