I'm not sure whether you are suggesting that the trial may have...

I'm not sure whether you are suggesting that the trial may have achieved "overwhelming efficacy" but the decision-maker chose not to terminate early. I just cannot see it myself. Given the desperate situation in the US, the idea that a well designed and conducted clinical trial with pre-specified values permitting early termination for overwhelming efficacy would not be terminated at the earliest opportunity if those values were achieved is hard to believe. What's in the interests of the FDA, NIH and MSB in the current environment (not to mention the patients receiving placebo) is to get a proven treatment out there ASAP. Let's assume they were to achieve overwhelming efficacy at the next two stopping points? Would it be a good thing for the trial to continue in those circumstances? How many lives might that cost? This is where the ethical issue arises.

Leaving aside the cost in terms of lives lost, if the trial was allowed to continue even though overwhelming efficacy was proven, I completely agree there are advantages in having the trial run its full course. For one thing, we would get a more accurate measure of the effect on mortality and the other important endpoints. Clinicians will also find the results more persuasive because, as most of them will be aware, studies have shown that trials stopped early for overwhelming efficacy often overstate the effect size, sometimes quite substantially.