I'm not sure about Mennonites. One of their communities writes about it and seems to suggest only 1 of the 40 or so communities is hardliners against vaccination. But I also note this is written in a really neutral way (could be to placate government, dunno): https://www.mennoniteusa.org/measles/
They never really stopped, it's been every few years since then: https://forward.com/news/417390/measles-is-hitting-ultra-ort...
The Amish are/were undervaccinated but it wasn't due to religious objections. It just seems uncommon in communities to see a dr, unless it's needed: https://www.pbs.org/newshour/health/ohio-amish-reconsider-va... It's also hard to get an official count (I've seen estimates below 20% vs almost 90% for non-amish communities in same state, but then you read stuff like this which suggests even the old older is above 80% https://publications.aap.org/pediatrics/article-abstract/128... ) since these communities are grandfathered into their own healthcare systems and often exempt from the normal federal welfare systems: https://www.ssa.gov/faqs/en/questions/KA-02411.html
I'm not sure about Mennonites. One of their communities writes about it and seems to suggest only 1 of the 40 or so communities is hardliners against vaccination. But I also note this is written in a really neutral way (could be to placate government, dunno): https://www.mennoniteusa.org/measles/