Most states report to the Centers for Disease Control and Prevention (CDC) every year on the vaccine coverage of children entering kindergarten, including how many children are immunized against diseases such as hepatitis B, diphtheria, tetanus, pertussis, polio, measles, rubella, varicella, and mumps.

State laws requiring proof of vaccination at school entry have been considered a safety net assuring that no child in the United States will be missed. The safety net relies on schoolteachers, health department staff, and others to identify children who are not up-to-date with their vaccinations. "Findings of nationwide coverage in recent years underscore the success of school entry requirement vaccination coverage, which increased substantially when entry requirements were established," the CDC said in a report on vaccination coverage in the 2005-2006 school year.

But the goal of universal coverage may be harder to realize in the future, as more and more states offer nonmedical exemptions to the vaccination requirement, say researchers who looked into the effects of exemptions on one particular disease—pertussis—which remains endemic in the United States and has been increasing during the past decade.

The researchers point out that at one time, parents were required to show that they held and practiced religious beliefs that prevented vaccination of their children. Increasingly, however, states—19 as of March 2006--are allowing "personal belief" exemptions,  which can include philosophical or other unspecified nonmedical reasons for refusing vaccination. In some states, such as Maryland and California, personal belief exemptions are very easy to obtain, requiring only a parental signature on a preprinted statement. Other states have some administrative requirements, such as notarization or a personal appearance or letter by the parent.

To try to determine the effect of nonmedical exemptions in general and "personal belief" exemptions in particular, the researchers analyzed state-level exemption rates for school years 1991-92 through 2004-05. In those years, all states except Mississippi and West Virginia allowed religious exemptions, and 19 allowed "personal belief" exemptions.

Using a complex research model, the investigators examined school data on the disease of primary interest to them—pertussis. What they found was that states where personal belief exemptions exist and are easily obtained had higher exemption rates and greater incidence of pertussis than those with religious exemptions only. Pertussis incidence in states allowing personal belief exemptions was more than twice as high as in states that allowed only religious exemptions. States with easy procedures for granting personal belief exemptions had a 90 percent higher incidence of pertussis.

 "These study findings indicate that state exemption policies affect exemption rates as well as pertussis incidence," they said.

Because children with exemptions from vaccination are at increased risk of disease and more likely to communicate disease to others, states may need to take another look at their immunization policies, on public health grounds, the researchers suggested. "State-level policies on nonmedical exemptions and documentation of immunization status should be viewed as part of the efforts to control or eliminate vaccine-preventable diseases."

The research report, "Nonmedical Exemptions to School Immunization Requirements," appeared in the October 11, 2006, issue of the Journal of the American Medical Association. The corresponding author can be contacted at das@ehpr.ufl.edu.

The CDC report on vaccination coverage in 2005-06 can be read at http://www.cdc.gov/mmwr/, October 20, 2006.

See also: "The Politics of School Immunization" at http://www.healthinschools.org/ejournal/2005/may1.htm and "Are Schools a Factor When Parents Refuse Immunization?" at http://www.healthinschools.org/ejournal/2004/july3.htm.