Similarly if we revert to prepandemic social interaction (e.g. large indoor venues, crowded offices, etc) we will have Delta and other congtagious variants. Won't matter how many people have natural or vaccine-induced immunity. They will be infected and reinfected.
I am not saying anything. I am just pointing you to someone that has more knowledge than me. Speaking of measles, I came down with a second variant in boot camp(German measles) after being vaccinated as a child.
We have, or had herd immunity against measles and for a time Measles was considered irradicated in the US, until a number of people in the US and in some European counties stopped getting their children vaccinated for it because of fears that the MMR vaccine caused autism, which it doesn’t and among groups of certain religious sects who do not vaccinate.
I agree that border controls are important. But several of the most recent outbreaks in the US were traced to unvaccinated US citizens, mostly Orthodox Jews who traveled to Israel and Amish missionaries who travelled to the Philippines where Measles is endemic and brought it back with them.
While the outbreaks were mostly confined to their close-knit communities, there were cases that showed up outside of those communities through casual contact among the unvaccinated who are unvaccinated for reasons other than religion.