Actually - the Amish have been extremely resistant to vaccination from the beginning of the practice.
Just a simple search of "vaccination Amish" revealed the following:
http://www.avn.org.au/Vaccination%20Information/Measles_casestudies.htm
Which actually mentions the lack of vaccinations among the Amish.
And then this from another site:
Vaccinators failed to eradicate measles, so now they claim success in reducing measles incidence between 1970 and 1987. However, it has been published that the very unvaccinated Amish communities did not report a single case of measles between 1970 and 1987. Then, since 1987, both the unvaccinated Amish and the well vaccinated outside communities started experiencing huge outbreaks of measles. Quite obviously, vaccination was totally irrelevant. Quite likely, the sustained small outbreaks of measles between 1970-87 in the vaccinated was achieved by vaccination, which kept measles occurring.
(http://www.eaglefoundation.net/Hearings%20on%20HepB.htm)
Is it possible that the sudden appearance of measles in the Amish comes now from somewhat more contact between the two populations? The Indians before the Europeans arrived were completely measles free and then devastated by the disease after contact.