It seems that if one can refuse, then they do not 'HAVE to have them'?
The Vaccine Injury Compensation Program started by Congress some years ago doesn't have nearly the money or manpower to deal with all of the injuries and deaths should vaccines be compulsory for children. I've listed all this info before here, but even if you attend Harvard Medical School, for example, the med school cannot force you to be immunised. The school cannot bear that sort of liability. It HAS to be laid on the shoulders of the individual himself, or in this case, the parents.
Which is why every physician should be giving parents the manufacturer's insert for the particular vaccine. A parent MUST make an informed decision in this matter, with the manufacturer's warnings, list of adverse reactions and frequency observed in clinical trials, etc. The parent is ultimately liable if their child is injured or killed by the vaccine, or has an allergy to eggs (Chicken Pox vaccine cannot be administered in that case)...the parent bears the liability.
The list of exemptions vary by state in the US. In each and every state in the US, medical exemption exists. The other two are religious and philosophical. Most school intake forms have a box to tick to decline immunisations, and list the exemption. Or a parent can submit a short letter stating that choice.