——During flu season there is basically no excess capacity. ——
The patients occupying the ICU beds are in effect isolated to prevent the spread of their pneumonia. Deaths mostly result from pneumonia rather than flu. Flu is the precursor
We don’t put patient in ICU beds to isolate them.
We put people in ICU beds because they need critical care.
Most do end up with a secondary bacterial pneumonia, but some have viral pneumonia or some other complication from the flu.
The point is there is no excess capacity for a novel infection if significant numbers of people get infected and need ICU care to survive.