CDC Internal Report Calls Delta Variant as Contagious as Chickenpox

1) Vaccination efforts have been spread out over a rather long time, which is kind of a worst-case. This isn't a unique worst case (natural immunity is sometimes similar), but we kind of picked the worst-case schedule.

2) We have a situation where ~50% of the world is vaccinated and ~50% is unvaccinated, which is kind of a worst-case.

3) Vaccines produce a much stronger response than natural immunity.

Normally, with a high-spread virus like COVID19, everyone in a community would catch it, some would die, and we'd all develop natural immunity at roughly the same time. From there on, there would no longer be much selective pressure, since there wouldn't be much virus to mutate.

With vaccinations, we have a giant pool of virus (in the unvaccinated) right next to a giant pool of immune individuals (the vaccinated) for what's likely to be years. The vaccinated individuals, at least in my community, are taking literally no precautions against spread -- even casual ones.