How long since routine smallpox vaccinations were given to everyone? There must be millions of Americans unprotected.
It was declared eradicated globally in 1980.
When it was endemic it would appear in cycles, mostly affecting the smallpox naive young. Older kids and adults mostly had had it so were spared. Strong, quick, youthful immune responses spared about 70% from dying. When smallpox naive entire populations got infected the death rates were MUCH higher, up to 90%, eg. Hawaii, Easter Island, Aztecs and Incas, and presumably current US.
Before Jenner discovered ‘cowpox’ vaccination in 1796, a somewhat similar preventative was Variolation—intentional inoculation with live smallpox. Initially promoted in the colonies by Cotton Mather, who first learned of it from his wise slave, Onesimas, then later read overseas medical articles on it. He promoted it when smallpox next hit Boston in 1721, resulting in dramatically fewer than expected deaths. Boston then promoted it across the colonies. In 1775, after smallpox prevented an American capture of Quebec, Washington mandated variolation for the continental army, with approval of, amongst others, Patrick Henry. Variolation caused about one tenth the death rate of naturally acquired smallpox, about 3%. Die soon 3%, when the chances of avoiding smallpox were trivial and thus the alternative was die later 30+%, was a winning bet. The lower rate may in part have been from a low initial viral dose and from the virus being weakened by the process. But mostly the low rate resulted from starting the infection via the arm skin instead of via inhalation. The disease spread slower from there, allowing enough time for a successful immune response.