You are missing a very important scientific aspect. In addition to time being important, type of virus is important. Single stranded DNA viruses (Covid, flu) with little or no outer protection mutate like crazy. That is why the flu vaccine is new every year, that is why the Covid virus mutates once per 2 people that get it.

That means that early 95% vaccine effectiveness drops very rapidly as the virus mutates, and so the post-vaccine period for Covid is also one of a lot less vaccine effectiveness than the post-vaccine world for smallpox.