That news appears in the Oct. 11 issue of The Journal of the American Medical Association.
"States should examine their exemption policies to ensure control of pertussis [whooping cough] and other vaccine-preventable diseases," write the researchers.
They included Saad Omer, MBBS, MPH, of Johns Hopkins Bloomberg School of Public Health.
Omer and colleagues studied states' vaccine requirements for students aged 18 and younger, as well as states' whooping cough rates as reported to the CDC from 1986 to 2004.
Nationwide, all students entering school are required to "provide documentation that they have met the state vaccine requirements," the researchers write.
But all over the U.S. -- except in Mississippi and West Virginia -- students may skip vaccines for nonmedical reasons, Omer's team notes.
Most of the states allow vaccine exemptions for "religious" reasons. Fewer states allow exemptions for "personal belief."
Vaccine exemptions are easier to get in some states than in others, the researchers also point out.
Whooping cough rates were higher in states with "personal belief" exemptions and in states with easier vaccine exemption processes, the study shows.
The CDC's data might not reflect all whooping cough cases, which often go unreported. That could have swayed the results, Omer's team notes.
The researchers call for a balance between personal freedom and public health, with regard to vaccine policies.
"States must balance parental autonomy with the tremendous public health benefit of vaccines when considering the types of exemptions allowed and how policies are implemented," write Omer and colleagues.
SOURCES: Omer, S. The Journal of the American Medical Association, Oct. 11, 2006; vol 296: pp 1757-1763. News release, JAMA/Archives.
By Miranda Hitti
Reviewed by Louise Chang