Yes it is being done. I know because a couple I know were in the initial trials for the first Pfizer vaccine. They both got the real shot, revealed later to them. Again, they were in the new booster trials early(?) last year and one got the real shot and the other didn’t, revealed later and the placebo person immediately got the real shot the week they came out. Both are 65+ with one having had cancer a few years ago and other problems, the other pretty healthy and an avid hiker.
Mike