Smallpox vaccines were quite controversial at the time and opponents went for much the same disinformation tactics as with the covid vaccines. For example, rumo

Smallpox vaccines were quite controversial at the time and opponents went for much the same disinformation tactics as with the covid vaccines. For example, rumors that cow heads would start sprouting from your body were published (https://www.npr.org/sections/goatsandsoda/2015/01/07/375598652/a-cow-head-will-not-erupt-from-your-body-if-you-get-a-smallpox-vaccine https://www.npr.org/sections/goatsandsoda/2015/01/07/3755986...) in popular media. There were also Church leaders saying that it was immoral to intervene in God's will in this way: if He decided you should get smallpox then that was your fate. It's not so far from people fearing that COVID vaccines were full of microchips to control your brains, or that it was all a mass sterilization campaign organized by the deep state or whatever.