The traditional Amish do not vaccinate. And they are a tight knit community. So they are the perfect placebo cohort. We just compare the rate of death of the unvaccinated Amish with the rate of death of people in the same area.
I recently learned that it’s likely that in the >50,000 person unvaccinated Amish community in Lancaster, PA there are less than a handful of people who died from COVID. Lancaster is the largest Amish community in the US.