Saad Omer of Emory University and his colleagues reviewed the proposed legislation, all of which did not pass and were not signed into law.
"School immunization mandates, implemented through state-level legislation, have played an important role in maintaining high immunization coverage in the United States," the study said.
The researchers organized the bills by exemption type such as religious, personal belief and medical. The study showed that certain types of exemptions and the ease of obtaining them can help predict risk of disease among people who use their exemptions and their communities.
The bills were further organized by the presence of an administration requirement, which was defined as an action required by parents beyond signing a form to act on an exemption. Fifteen bills did not have administration requirement, seven had one or two requirements and 14 had between three and five requirements.
Of the 36 bills that were introduced, five restricted exemptions and 31 expanded exemptions. None of the bills that proposed expanding exemptions were passed.
"Exemptions to school immunization requirements continue to be an issue for discussion and debate in many state legislatures," the study's authors said.