Doctors can also be incentivized to do rotations in the ER. My primary care physician many years ago used to do ER rotations as a sort of overtime. Inventivize with the right pay, more will do it. Granted this isn't a large labor supply, but it certainly could help.
Instead, what you see is a shrinking of the nurse labor supply by a few percentage points due to vaccination requirements. Pretty ridiculous to complain about lack of capacity when you force some of that because you refuse to officially recognize natural immunity as equal to vaccine derived immunity.