Receiving multiple vaccines during childhood doesn't damage the immune system and make kids more vulnerable to diseases that aren't covered by the immunizations, researchers reported yesterday in the first US study to test the association.
Experts say the findings offer reassurance, which comes against a backdrop of parent concerns about their children's vaccines that in recent years have been fanned by the antivaccine movement. Researchers from Kaiser Permanente and the US Centers for Disease Control and Prevention (CDC) reported their findings in the Journal of the American Medical Association (JAMA).
In 2002, the Institute of Medicine (IOM) examined questions about whether getting multiple vaccinations could impair developing immune systems, which led them to reject, among other considerations, that exposure to multiple vaccines caused nontargeted diseases. The agency noted, however, that a relationship between multiple vaccinations and the risk of nontargeted infections was biologically plausible.
Since then, researchers have looked at questions related to multiple vaccinations and autoimmunity and allergy, but little work has been done to examine the association between multiple vaccine and nontargeted infections, and none involved the current US childhood vaccine schedule.
Large study with 12 years' of data
In the new study, the investigators studied children enrolled in six healthcare organizations that are part of the Vaccine Safety Datalink (VSD), a collaboration funded by the CDC that uses electronic health record databases to study vaccine safety.
The team selected a random sample of 193 children who had been diagnosed as having infections not targeted by the vaccines and a control group of 751 kids who had not been diagnosed with the infections. Their study population was drawn from 500,000 infants from birth to 47 months over a 12-year period.
The researchers estimated exposure to vaccine antigen through the first 23 months of life in kids with non-vaccine targeted infections from ages 24 months through 47 months who were treated in emergency departments or were hospitalized. Then they compared the findings with kids who didn't get sick with nontargeted infections.
Cumulative antigen exposure was 240.67 for children seen for nontargeted infections and 242.9 for controls who weren't diagnosed with the nontargeted illnesses. Researchers also looked for any possible association between maximum single-day antigen exposure and the risk of nontargeted infections. Again, they found no statistically significant difference.
No evidence of immune overload
Jason Glanz, PhD, the study's lead author and senior investigator at the Kaiser Permanente Colorado Institute for Health Research, said in a Kaiser press release yesterday that the findings suggests that the theory of overloading an infant's immune system is highly unlikely.
"Parents have genuine concerns about their children's safety as related to vaccination. We hope this study shines some light on their concerns, helping parents across the nation better understand the safety and benefits of vaccinating on time," he said.
Study coauthor Matthew Daley, MD, said parents' concerns and questions are understandable, and the study reassuringly found that vaccination didn't appear to damage the immune system in a way that makes them prone to other types of infections. "Parents who may be hesitant to vaccinate should bring up their concerns with their pediatrician or family physician—we are eager to discuss the benefits of vaccination. Vaccines not only protect children, but others in the community who may be more vulnerable to vaccine-preventable diseases," he said.
More efforts needed to build confidence
In an accompanying editorial in the same issue of JAMA, two pediatricians not involved in the research write that the study provides robust and reassuring results. The authors are Sean O'Leary, MD, MPH, with the University of Colorado Anschutz Medical Campus in Aurora, and Yvonne Maldonado, MD, with the Stanford University School of Medicine in California.
They also said the results offers further reassurance about the safety of the nation's vaccine schedule. O'Leary and Maldonado acknowledged that the investigations faced a tough challenge in how to define the term "schedule," which isn't well-defined in the medical literature. They said the team settled on a reasonable definition to satisfy clinicians as well as parents and primary care providers by using cumulative antigen exposure as a proxy for schedule, a technique that may be useful for future studies involving vaccination schedules.
Future studies should look at different antigen mechanisms and their possible interactions, the two added.
The study, they wrote, provides further reassurance that the US childhood vaccine schedule is safe regarding increased risk of nontargeted infections, "yet the small but vocal minority of antivaccine groups may not be satisfied by the evidence provided through VSD and other vaccine safety surveillance."
Despite the promising findings, more efforts are needed to strengthen the public's confidence in vaccines, they added, noting that confidence-building is the VSD's second purpose and was similarly voiced in a lead recommendation from a 2012 follow-up IOM report on the safety of the childhood immunization schedule.
"Simply providing scientific information and assuming parents will make the decision to vaccinate is not enough," the authors wrote. "Delivering evidence-based information to parents and clinicians in ways that inspire confidence in the robust and safe childhood immunization schedule is critical for maintaining the health of children."
Mar 6 JAMA abstract
Mar 6 JAMA editorial
Mar 6 Kaiser Permanente press release