The thing is I can't think of a single legitimate reason why they would not vaccinate their kids aside from them just not believing in science.  

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I mentioned that not vaccinating their kids is a huge sin for a variety of reasons. For starters there is the immediate danger of their kids potentially dying from an otherwise completely preventable disease. The Torah values human life above almost anything to the point where aside from 3 very specific sins, if somebody's life is in danger, we are REQUIRED to assist when possible. Because not vaccinating their kids would potentially be putting them in danger, that would be a massive sin. There's also the fact that doing so puts other people's lives in danger making it an even bigger sin. Another sin is the fact that not vaccinating their kids makes the jewish community look bad which is a sin called a  חילול השם (Hilol Hashem. Probably screwed up the spelling btw). In Judaism because we've been persecuted for thousands of years, the rabbis teach us to always act in a way that reflects well on the jewish community since a single jew doing something dumb will make us all look bad (as you can see from this situation). Because of this, doing something publicly that reflects poorly on the Jewish community is a massive sin.  

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The dumbest part about all this is that Judaism isn't anti-science. Even the ultra-orthadox jews (the crazy super rabbis who's literal job it is to study the torah practically 24/7) are not anti-science so I have no idea why these morons would think they either can't or shouldn't vaccinate their kids.  

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I hope that answered your question (\^\_\^)