I just watched a zombie movie and the premise was that they became zombies because they received a vaccine after a pandemic and one of the chemicals(?) in the vaccine mutated. Luckily, only a small percentage of the population had been vaccinated before they realized what was happening.
It was one of those movies on youtube that don't list the title of the movie. I think it's under watch zombie movies in english free... something like that. lol
It wasn't a recent movie either it's at least 10 years old.