All states allow medical exemptions from vaccines because some people simply cannot get them. Immunocompromised children, for instance, wouldn't be able to handle the shot. Some states also allow parents to intervene based on religious beliefs, on the grounds that some sects would feel it was a violation of their beliefs to be forced to get the shot. That being said, according to the Vanderbilt University Medical Center there are only a handful of religions that have objections to vaccines: Christian Scientists, the Dutch Reformed Church (though not the modern American branch of that denomination, also known as the Reformed Church in America), and some faith healing denominations like Faith Tabernacle. However, many states also allow you to refuse vaccination by stating a personal objection.