Honestly, given human variability and immune system issues, I'd expect that some people would die from any injection given to millions, even if the injection was isotonic saline only. (I had a coworker who welted up any time an aluminum needle was stuck in him. Made TB testing amusing.)
That one or two humans per million would have a nasty, possibly fatal immune response doesn't get anywhere close to the number of people dying before a vaccine was available.