You can block it. The unit won't heat or cool that room anymore though. The return air does effect supply air temp. And heat pump efficiency. With a 60 degree return air temp, the heat pump is more efficient then with a 70 degree return air temp.
We are simply getting contaminated causing otherwise healthy folks to lose the function of their kidneys and for a senior citizen who is already suffering sarcopenia this can be a death sentence because of the complexities associated with Renal Failure.
Thus, a government incarcerating people in a prison under such deadly conditions that they die in a few years is murder by the state--democide--as would parents letting a child die from malnutrition and exposure be murder. So would government forced labor that kills a person within months or a couple of years be murder.