A small number of humans.
Based on what I have read, the investigators have given the vaccines too animals.
In my earlier years, I was part of a vaccine trial on mice (as a lab tech). IIRC we had to introduce the vaccine at various dosages as well as different timelines, so that when we infected them we could count how effective the vaccine was at those various dosages and various start dates. I recall that it may have even been close to a year before we actually infected these mice, but maybe it was only 6 months worth of prepping the mice. Now this was for a bacteria, not a virus, for that particular trial, but I would assume that viruses may be handled in a similar way. I worry that we haven’t given our test animals enough time in these trials, but I guess that’s not for me to say. I don’t know one way or the other. I’m just saying, I have concerns, and I think they are valid concerns.
Mask wearers say let’s be safe, not sorry. I think testing vaccines certainly falls into that category.