[jrochkind1]

Not every single study is blinded -- sometimes there are ethical reasons that lead against it. And you can have a valid study without it sometimes.

But looking up this one, it was blinded, indeed! https://www.henryford.com/moderna-vaccine/faqs

Even if it isn't blinded, you try to make sure the control group and experimental group are equally representative though, you don't "put all the X in the Y group" ever, this is true! Because the whole point is testing two groups as much alike as possible other than the thing you are testing.