That's the version that killed smallpox too. Earlier vaccines against it were worse, including some that could give you smallpox, even fatally (but you were less likely to get sick from it than from exposure, and you were less likely to get as sick if you got it from the vaccine than naturally catching it). The vaccine was always controversial, but eventually it became safe enough that enough people became comfortable with it being forced on everyone. This is the first disease we developed vaccination for, and for good reason, it was a gross, painful, deadly, and very infectious disease. If it were still around I'd be first in line for a vaccine even with the blister.