It should be but multiple states are pushing legislation to remove the exemptions that allows children to remain in school if their parents elect not to vaccinate.
Then under another law the school is required to provide a fair and appropriate education regardless of disability. Just need to have unvaccinated children determined to be disability.
Even if those laws passed, the decision would still be in the hands of the parents, that legislation would just stop them from jeopardizing other children in the public school system.