The vaccine was tested for creation of a specific immune response which was believed to fight an infection. It was never tested to "prevent infection" and never tested to stop transmission. That's the marketing mantra, not the science. Exactly the same is true of polio, measles, and yes, COVID.
Re "Smallpox vaccination was said to prevent infection with smallpox." Nope. That's not what the clinical study said. It's public here: section 6.1.
https://www.fda.gov/media/75792/download
The vaccine was tested for creation of a specific immune response which was believed to fight an infection. It was never tested to "prevent infection" and never tested to stop transmission. That's the marketing mantra, not the science. Exactly the same is true of polio, measles, and yes, COVID.