All 50 states allow medical exemption from vaccination. Medical vaccination exemptions have been in place for a long time for people who are immunocompromised (with weakened immune system) or for various other conditions that make getting vaccinated dangerous. These are necessary exemptions, however they leave very sick people vulnerable to disease.
Over the last decade many states across the US have been allowing nonmedical exemptions including those for religious rights and philosophical opposition. Your right to nomedical exemption is based on your state’s exemption laws. And in some states there is also the possibility of exemption based on proof of immunity to a disease.
As of 2016, all U.S. states allow a religious exemption to vaccination except California, Mississippi and West Virginia.
The rise of nonmedical exemption is leaving large pockets of unvaccinated individuals in many states–places where there is higher risk and incidence of preventable disease.

Source: CDC 2009-10 through 2015-16 School Year Vaccination Exemptions Trend Report | 2010 data is not available GIF / Youtube
The good news?