Senti,
I think it was clear that after the halt all patients added to the trial received the vaccine and they reduced the total number by those who otherwise would have received the placebo. By the time the decision was made, and the trial resumed to add people, all that were in the trial in the control group would have crossed over if they wished. I suspect we'll find that all who didn't cross over either died, or were too ill to do so by the time they had the opportunity, but we'll only know that when we get the data.
During the halt I'm sure that those already in the trial would have continued to be treated just as though the trial was continuing. No doubt many lined up to initiate the trial at the time of the halt were no longer eligible by the time the trial resumed.
I don't know if at the time of the halt the company and the regulators discussed changing the primary goal to overall survival, but clearly that wouldn't be something you'd want in a trial where the control could cross over on progression.
In the past I've seen trials that went bad because control patients lived longer than historical data justified. I believe it was clear that many of these people used other therapeutics once progression was determined and they did gain benefits. The drug in question was abandoned, I suspect it would have been approved if based on historical information. It did produce results that were better than the control, just not better enough.
Gary
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