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a lot of famous people opposed vaccine for smallpox in the early 1900s, and I should note that vaccinia did have a small but sometimes fatal side effect.
However, smallpox was highly fatal and the use of using mild smallpox pus to vaccinate people before Jenner found cowpox worked was a big debate in the 1700
Lady Montague helped popularize this in England after she saw it used by the Turks. But in the USA, the practice was introduced by Cotton Mather (yes the one behind the witch trials who later repented) because his black slave told him how it was used in Africa.
and one reason Canada is not part of the US was because the American army had many smallpox casualties. However, George Washington knew about innoculation and implemented smallpox innoculation of his army.