An analysis of several studies of measles and pertussis outbreaks in the United States suggests that when parents refuse vaccinations for their children or for themselves, they contribute largely to outbreaks of those diseases.
For a new study published in the Journal of the American Medical Association, researchers searched the medical literature for reports of US measles outbreaks that have occurred since measles was declared eliminated in the United States (after January 1, 2000), endemic and epidemic pertussis since the lowest point in US pertussis incidence (after January 1, 1977), and for studies that assessed disease risk in the context of vaccine delay or exemption.
Among 32 reports of pertussis outbreaks, which included 10,609 individuals for whom vaccination status was reported (ages 10 days to 87 years), the five largest statewide epidemics included substantial proportions (24 to 45 percent) of people who were unvaccinated or undervaccinated.
However, several pertussis outbreaks also occurred in highly vaccinated populations, indicating waning immunity. Nine reports (describing 12 outbreaks) provided detailed vaccination data on unimmunized cases; among eight of these outbreaks, 59 to 93 percent of unvaccinated individuals were intentionally unvaccinated.
“This review has broad implications for vaccine practice and policy,” says Saad Omer, professor of global health at Emory University’s Rollins School of Public Health.
“For instance, fundamental to the strength and legitimacy of justifications to override parental decisions to refuse a vaccine for their child is a clear demonstration that the risks and harms to the child of remaining unimmunized are substantial. Similarly, central to any justification to restrict individual freedom by mandating vaccines to prevent harm to others is an understanding of the nature and magnitude of these risks and harms.
“Our report shows that outbreaks of vaccine-preventable diseases in the United States have prompted clinicians, public health officials, and the public to pay greater attention to the growing phenomenon of vaccine refusal and hesitancy. We believe this study will result in an improved understanding of the association between vaccine refusal and the epidemiology of these diseases.”
Source: Emory University