The Amish do vaccinate. The old Amish communities have a lower rate than other communities, but the rates are steady in most communities. There are, however, almost a dozen "Amish" types, from those speaking a form of German to those that trade with "English" neighbors and are active in local counties while still living within their own village.
About 70% of the Amish in Lancaster County do, indeed, vaccinate.
Immunization can be especially low among conservative groups, with only 6% of Swartentruber Amish participating, compared to 63% of the overall Amish population and 85% of the non-Amish population, according to a 1984 study (Paradox, Hurst/McConnell).The German-speaking Amish do have autism, at a rate of approximately 1:250 to 1:200, which is lower than the national average, but oddly close to the rates in other parts of rural PA, OH, and WV. So, that leads to other questions about clusters of autism and why some areas have substantially lower diagnostic rates -- with or without vaccination.