More than 50% of recent measles cases in the United States occurred in children whose parents refused vaccination, and at least a quarter of pertussis cases in the five largest statewide outbreaks also occurred in unvaccinated or undervaccinated individuals, according to a literature review published in the March 15 issue of JAMA.
"This review has broad implications for vaccine practice and policy," study author Varun K. Phadke, MD, from Emory University in Atlanta, Georgia, and colleagues write. "Vaccine refusal–specific strategies to optimize vaccine uptake could include state or school-level enforcement of vaccine mandates, or increasing the difficulty with which vaccine exemptions can be obtained."
Dr Phadke and colleagues examined the role of vaccine refusal in the recent outbreaks of measles and pertussis, using population-level vaccine exemption rates as a measure of vaccine refusal.
The authors identified 18 measles studies, all conducted after measles was declared eliminated in the United States in January 2000, and 32 pertussis outbreak studies, published in the PubMed database after the nadir of this disease in 1977. The review did not include a formal assessment of the quality of the identified studies.
The measles studies included 1416 cases documented since 2000. The researchers found that more than half of these cases (56.8%) occurred in children whose parents refused measles vaccination. And in the pertussis studies, many of the cases (24% - 45%) in the five largest statewide pertussis outbreaks occurred in unvaccinated or undervaccinated individuals.
In addition, both the measles and pertussis outbreaks occurred not only among unvaccinated individuals but also among vaccinated individuals in geographic locations with a high prevalence of vaccine exemptions.
The authors suggest that this pattern may reflect the fact that vaccine refusal and waning immunity are intertwined: nonmedical exemptions for childhood vaccination increase the risk for infection of individuals with waning immunity.
The Need for a Centralized Infrastructure
The research is yet another demonstration that a child who is unimmunized is at risk for harm. It also underscores the need for an infrastructure that can reliably deliver vaccines, writes Matthew M. Davis, MD, from the University of Michigan in Ann Arbor, in an accompanying editorial. He argues that the United States must prioritize the establishment of a highly reliable vaccination program.
"Without a centralized infrastructure focused on the goal of maximizing community immunity, high-reliability vaccine coverage remains challenging in the United States," he writes. "Nonetheless, if vaccines are developed for emerging diseases that threaten the US population — such as Zika, Ebola, or human immunodeficiency virus — the public will likely expect the currently complex and heterogeneous vaccination system in the United States to function as a seamless organization. The US population wants vaccination to be safe, effective and available in a timely manner, and for immunization to be durable."
Dr Davis also recommends that vaccination programs borrow from the practices of the airline and nuclear power industries and create a culture of consistent and standardized practices that can deliver highly reliable performance.
One change that could promote this consistency would be for states to take a stricter approach to permissive exemption laws, he writes. Another would be for US vaccination efforts to focus on the issue of waning immunity by adjusting the recommended intervals between vaccines or developing novel vaccines with more durable immunity.
This work is supported by the Emory Vaccinology Training Program of the National Institute of Allergy and Infectious Diseases. One coauthor received grant funding from Crucell, Pfizer, and Merck and personal fees from Parents of Kids with Infectious Diseases. The other authors and Dr Davis have disclosed no relevant financial relationships.
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Cite this: Vaccine Refusal Puts Unvaccinated and Vaccinated at Risk - Medscape - Mar 16, 2016.