Ask to speak to an occupational health doctor at the medical school to which you are accepted. This is routine stuff that they handle.
According to what I've learned today on my occupational medicine rotation at a hospital with a measles outbreak going on at the moment, you do not need to be vaccinated if it's contraindicated for your health. If you are exposed then you can get IVIGs for post exposure prophylaxis. This is not my medical advice, get professional help about this.