This is why the trials are randomized and large enough to determine a difference.

Remember, neither doctors/nurses nor patient k ow who gets placebo and who gets leronlimab.

The treatments would look something like this in s/c:

Placebo arm: remdesevir, high flow oxygen/intubation, dexamethasone, saline/placebo injection

Therapeutic/leronlimab arm: remdesivir, high flow oxygen/intubation, dexamethasone/other steroid, leronlimab injection.

The only variable/difference between the groups is leronlimab vs placebo/saline injection.

There may be variation among treatment of patients (anticoagulants, antibiotics for secondary infections, dialysis, etc), but as patients are randomizes into one of the two arms, these are presumed to not affect the outcome.

I hope that helps. Others here can correct any mistakes, but that is the basis of trial construction.