Most states do not "require" you to belong to a practicing organized religion that supports your practices, but often times universities will ask you for a reason to support your claim. Religious exemptions are legal in every state except Mississippi and West Virginia.
The exemption below is acceptable in accordance to Missouri state laws. You will need to research your states laws before deciding weather or not to copy and use this letter for yourself. The most comprehensive vaccine exemption information I have found is located here
To whom in may concern,
This written statement is to exempt myself from the immunization requirement, and the Mantoux (PPD) Tuberculin Test, because I hold genuine and sincere personal religious beliefs which are inconsistent with these medical procedures and experimentation. The practice of vaccination and the injection of any foreign substance is contrary to my conscientiously held religious beliefs and practices, and violates the free exercise of my religious principles.
All vaccines are made in violation of God’s word. Vaccines are made with toxic chemicals that are injected into the bloodstream by vaccination. All vaccines are made with foreign proteins (viruses and bacteria), and some vaccines are made with genetically engineered viral and bacterial materials.
I believe that man is made in God’s image and the injection of toxic chemicals and foreign proteins into the bloodstream is a violation of God’s directive to keep the body/temple holy and free from impurities.
Vaccines are produced in animal tissues. I accept God’s warning not to mix the blood of man with the blood of animals. Some vaccines are even produced in aborted fetal tissue.
The acceptance of these vaccines promotes abortion and violates the Sixth Commandment of "Thou Shall Not Kill".
Applicable law has been interpreted to mean that a religious belief is subject to protection even though no religious group espouses such beliefs or the fact that the religious group to which the individual professes to belong may not advocate or require such belief. Title VII of the Civil Rights Act of 1964 as amended Nov. 1, 1980; Part 1605.1-Guidelines on Discrimination Because of Religion.