For most, it's misinformation and scare tactics/articles. For example, with the Orthodox Jews in NY, they really don't like listening to the government, town, city, county, state, and even the federal government. They live in highly insular communities and turn their nose to outsiders much of the time. They trust their rabbis closely and because of that, their word is effectively law. So if a rabbi decides that a campaign by NYC and NY state to push for vaccinations is apparently a ruse of the Germans, then the majority in that community will follow along without questioning it.
Orthodox Jewish communities are like Islamic communities only with far less violence and more welfare manipulation.