In what may seem like common sense to many parents, children who aren't vaccinated for measles or pertussis are more likely to get those diseases, according to a new study by an Atlanta researcher and other doctors published in the Journal of the American Medical Association.
"The phenomenon of vaccine refusal was associated with an increased risk for measles among people who refuse vaccines and among fully vaccinated individuals," study author Dr. Varun K. Phadke, of Emory University, and colleagues wrote. "Although pertussis resurgence has been attributed to waning immunity and other factors, vaccine refusal was still associated with an increased risk for pertussis in some populations."
More than 50 percent of recent measles cases in the United States occurred in children whose parents refused to have them vaccinated, researchers found.
Also, at least a quarter of pertussis cases in the five largest statewide outbreaks occurred in those who were not vaccinated or were under-vaccinated.
Parents are refusing vaccinations due to religion beliefs or for moral or philosophical reasons, researchers wrote. During the past 20 years the rate of parents refusing vaccinations has increased both in states with lax procedures for obtaining exemptions and those with stricter rules, according to the study.
"Many childhood vaccine-preventable diseases have been effectively controlled," the doctors wrote in the study. "However, recent outbreaks of vaccine-preventable diseases in the United States have prompted clinicians, public health officials, politicians, the media, and the public to pay greater attention to the growing phenomenon of vaccine refusal and hesitancy."
In 2000, measles was declared eliminated in the United States. In 2014, there were 23 measles outbreaks, including one that started in Disneyland in Anaheim, Calif., and 668 measles cases are reported in the nation, according to the study.
Although measles is making a comeback, pertussis has never been eliminated. The disease was declared an epidemic in 2010 when there were 9,154 reported cases in California, and again in 2014 when there are 9,935 cases.
The study suggests several reasons for the increase in cases: An increase in diagnostic techniques resulted in greater reporting of the disease, a new type of vaccine introduced in the 1990s was less effective than the old type, and a waning immunity in the population.
"This review has broad implications for vaccine practice and policy," the study stated.
The authors suggest policymakers should consider making it harder for parents to refuse vaccinations.
Those same policymakers and doctors should address why parents are hesitant to get their child vaccinated, the study authors said.
"Recognizing the limitations of the existing evidence should not stifle practitioners' and policy makers' ability to counsel families and craft effective policy, but should serve as motivation to develop, refine, and improve disease surveillance, detection, and outcomes-based research," the study stated.