There was a warning by some scientists that vaccinating during, rather than before, a pandemic would lead to mutant strains.
Dr. Dan Stock explained it to the Mount Vernon school board that if an animal reservoir existed for a virus it is nearly impossible to eradicate as was done with smallpox:
Whitetail deer have been identified as a reservoir in the United States, so vaccination might be hopeless:
https://freerepublic.com/focus/f-chat/3982073/posts
There are things that simply cannot be done.
Luc Montagnier said the same thing. But no one paid any attention to what he said.