If by secondary you mean bacterial infection around days 6, then that was one of the hypotheses and the reason for getting antibiotics (I have only taken antibiotics several times in the last 25 years). I also took a mild anti clotting agent (aspirin) as recommended by my doctor. Also I am 45 years old, so even though I am in a good physical shape (non obese, working out on a regular basis, not taking any medication apart from vitamins and herbs) and don't exactly qualify as young :).
Iirc two of the most effective prevention of death in clinical settings around here before vaccines and this new type of meds has been the introduction of antibiotics soon after admittance (for older patients) since it prevented bacterial pneumonias to occur opportunistically (many older early Covid victims died of this even if Covid was the initial infection). The second one was to put anti-clotting agents early on after admittance to prevent secondary issues due to clots.