I think you mean "smallpox and other viruses should already have evolved." The difference is that the smallpox vaccine prevented infection of the vaccinated. T

I think you mean "smallpox and other viruses should already have evolved." The difference is that the smallpox vaccine prevented infection of the vaccinated. That's not the case for existing SARS-CoV-2 vaccines. https://www.verywellhealth.com/covid-19-vaccines-and-sterilizing-immunity-5092148 https://www.verywellhealth.com/covid-19-vaccines-and-sterili... gives an approachable overview of the difference. Smallpox was eradicated. The likelihood of the same happening to SARS-CoV-2 is lower. At least, it would be the first example of a respiratory infection being eliminated. Influenza hasn't been eradicated and it does continue to evolve. More broadly, the idea of "immune escape" is hardly something I can lay claim to. You can read about it in existing literature.