Measles and pertussis risk higher for children with personal exemptions from immunization

December 25, 2000

Exemptors from vaccination also increase risk for some vaccinated children

CHICAGO -- Children who are exempt from immunization for religious or philosophical reasons have a higher risk of measles and pertussis, according to an article in the December 27 issue of The Journal of the American Medical Association. Parents and public health personnel should be aware of the risks involved in not vaccinating children and the potential impact on the community, the authors add.

Daniel R. Feikin, M.D., M.S.P.H., of the Centers for Disease Control and Prevention, Atlanta, and colleagues conducted a population-based, retrospective cohort study to evaluate whether personal exemption from immunization is associated with the risk of measles and pertussis at individual and community levels. They collected data on standardized forms regarding all reported measles and pertussis cases among children aged 3 to 18 in Colorado during 1987-1998.

According to background information cited in the study, 48 states allow exemptions from mandatory vaccination for religious reasons, and 15 states allow philosophical exemptions. Exemptions based on medical grounds are allowed in all states. A recent study showed that the risk of measles infection during 1985-1992 in the United States was, on average, 35 times greater in children with personal exemptions compared with vaccinated children.

In Colorado, the percentage of school-aged children who were unvaccinated as a result of personal exemptions in 1994 was 1.4 percent, more than twice the national average of 0.6 percent.

The authors assessed the relative risk of measles and pertussis among exemptors and vaccinated children, the association between incidence rates among vaccinated children and the frequency of exemptors in Colorado counties, the association between school outbreaks and the frequency of exemptors in schools, and the risk associated with exposure to an exemptor in measles outbreaks.

During 1987-1998, there were 45 cases of measles among exemptors aged 3-18 and 137 cases among similarly aged vaccinated children. From 1996-1998, there were 36 cases of pertussis among exemptors and 346 among vaccinated children aged 3-18. But since the total number of exemptor children was much smaller than the total number of vaccinated children, their risks of these infections were much greater.

"Exemptors were 22.2 times more likely to acquire measles and 5.9 times more likely to acquire pertussis than vaccinated children," they write.

"In children of day care and primary school age [age 3 to 10 years], in whom contact rates and susceptibility are higher, these risks were approximately 62-fold and 16-fold greater among exemptors for measles and pertussis, respectively," they continue.

The authors measured the impact of children with personal exemptions on community risk. "After adjusting for confounders, the frequency of exemptors in a county was associated with the incidence rate of measles [1.6 times greater risk] and pertussis [1.9 times greater risk] in vaccinated children," they write. Also, "schools with pertussis outbreaks had more exemptors (mean 4.3 percent of students) than schools without outbreaks (1.5 percent of students)," they continue. "At least 11 percent of vaccinated children in measles outbreaks acquired infection through contact with an exemptor."

The authors assert that the decision to forgo vaccination must balance individual rights with social responsibility. "If all vaccine-preventable diseases were confined to the individual (e.g., tetanus), the consequences of forgoing vaccination would fall only on the child whose parents made the decision. Most vaccine-preventable diseases, however, are spread from person to person. Therefore, the health of any individual in the community is intricately dependent on the health of the rest of that community," they write.

The authors believe parents making decisions regarding vaccination should understand the risks of not vaccinating their children, and they urge public health personnel to recognize the potential effect of exemptors in outbreaks in the community.
(JAMA. 2000; 284:3145-3150)

This release is reproduced verbatim and with permission from the American Medical Association as a service to reporters interested in health and behavioral change. For more information about The Journal of the American Medical Association or to obtain a copy of the study, please contact the American Medical Association's Science News Department at (312) 464-5374.

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