Yes. Some people have autoimmune diseases, where a vaccination would actually cause more harm than good. Regarding the philosophical aspect of this question, it would probably be better that it wasn't added as an exemption. The gray area here would be the religious aspect. I believe that as long as those who are 'religious exempt' are homeschooled or put in their specific religion's school, that, I would hope, there would be no contact of those children to any other children who are not able to have a vaccination due to medical problem. But I don't think any religion that puts children in harm should exist, such as those who prohibit vaccinations.