Ganymede25 t1_isd7j0z wrote on October 15, 2022 at 1:44 AM

Reply to comment by slouchingtoepiphany in Does a reverse placebo exist? by Nearby-Cloud-3476

That is interesting. I was in the Pfizer trial. When they unblinded us, the nurse that was giving us the results asked if we thought we had received the real thing or saline. At the time, she said that the participants were 100% correct. I don't know if that was an official question for the trial, but I think she just wanted to know if the guesses were correct.

slouchingtoepiphany t1_isd8rzm wrote on October 15, 2022 at 1:55 AM

I don't see how participants could have guessed correctly, unless everybody thought that they received the actual vaccine. In that case, the people who received active treatment were 100% correct and the people who received placebo were 100% wrong. Hmmm.

Ganymede25 t1_isdwn2m wrote on October 15, 2022 at 5:50 AM

Maybe it was because we were all paying a lot of attention to any details associated with the vaccine. For instance, both the experimental and control people would have pain at the injection site, but only people receiving the vaccine would have the injection pain go away and a new pain show up 6-12 hours later that would last for a day. That is the result of an immune reaction. Saline would not do this. When you combine the delayed pain with a slightly elevated body temperature and a slight headache, it is pretty easy to tell when you are sort of focused on whether you got the vaccine or not.

Regarding the 100% wrong for the placebo, maybe you got confused on my comment. In the trial, 50% of the people received the vaccine and 50% of the people received saline. The people who received the saline knew that they had no symptoms and were 100% correct that they didn't get the vaccine.

slouchingtoepiphany t1_ise8sfe wrote on October 15, 2022 at 8:39 AM

I did misunderstand your previous comment. It's conceivable that people who guess correctly had experienced delay hypersensitivity reactions at the injection site (with vaccine, but not with placebo), but it's also possible that the group of correct guessers was small, say 3-6, and with a smaller number it's easier to obtain a series of correct guesses by chance alone. It's like flipping a coin and having it come up heads 3-4 (or more) times in a row. Statistics can do that. However, I think it's more likely to be the delayed hypersensitivity reactions.