It was clear from context he was referring to rates of polio-induced paralysis, in an analogous theoretical scenario that doesn’t quite fit the actual history.
Your comment was interesting, though. I did some additional reading about the history of those vaccines.
Let me clarify: the polio vaccine is effective enough that after getting it, we all get to live our lives exactly the same way we would if polio didn't exist. You don't have to show proof of polio vaccination to keep your job or go in public places, and you don't have to take any other precautions to protect against polio.
Differing dynamics of diseases calling for different measures. We could go down a rabbit hole debating moot points.
The fact is the original comment as phrased was totally wrong, and we could debate the clarification.
Instead let’s just acknowledge that if smallpox were around today and we had a world wide epidemic but we had a vaccine that prevented ill effects in nearly all cases but still allowed transmission, then it’s safe to assume there would be vaccine mandate. That would be different dynamics just like polio. Different dynamic need different responses.
Never in history has there been such a widespread mandate for such a leaky vaccine. Saying there would be in a counterfactual world isn't a strong argument, especially since the smallpox vaccine was effective enough at stopping transmission that we were able to eradicate the disease.
Your comment was interesting, though. I did some additional reading about the history of those vaccines.