There is so much out there about vaccines — endless opinions and recommendations from doctors, experts, friends, family, celebrities, politicians — it can be challenging to identify who to trust and what to believe. Every parent’s only goal is to protect his or her child as best as they can. One of the most frequently asked questions is: “There are so many more vaccines than when I was a kid, will that overwhelm my baby’s system?”

A national survey (n=1,600) from the late 1990s showed that 25 percent of parents believed that their child’s immune system could become weakened as a result of too many immunizations and 23 percent thought that children got more immunizations than were good for them. These concerns have increased, and anti-vaccine groups would say “too many too soon.”

So, is exposure to multiple vaccines in the first months of life associated with an increased risk for infections that are not targeted by vaccines? No. Receiving multiple vaccines during childhood does NOT damage the immune system and make kids more vulnerable to diseases that are not covered by the immunizations.

This new study by researchers from Kaiser Permanente and the U.S. Centers for Disease Control and Prevention (CDC) reported their findings in the Journal of the American Medical Association (JAMA). The investigators studied children enrolled in health care organizations that are part of the Vaccine Safety Datalink (VSD), a collaborative project between CDC’s Immunization Safety Office and eight health care organizations. The VSD started in 1990 and used electronic health record databases to monitor the safety of vaccines and conduct studies about rare and severe adverse events following immunization.

“Some parents are concerned that multiple vaccines in early childhood could damage their child’s immune system, making them more susceptible to future infections. This new study suggests the theory of overloading an infant’s immune system is highly unlikely,” said Dr. Jason Glanz, lead study author and senior investigator at the Kaiser Permanente Colorado Institute for Health Research.

The investigators 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 half a million 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 results with kids who did not get sick with non-targeted infections. These infections included lower and upper respiratory infections, gastrointestinal infections and other viral and bacterial infections. Furthermore, researchers looked for any possible association between maximum single-day antigen exposure and the risk of non-targeted infections. For both, they found no statistically significant difference.

“It’s understandable that parents across the U.S. have questions and concerns about vaccine safety. This latest study found that vaccination didn’t appear to damage the immune system in a way that made kids more infection-prone. This finding will hopefully provide additional reassurance to parents about the safety of the recommended schedule,” said Dr. Matthew F. Daley, a co-author, Kaiser Permanente pediatrician.

In an editorial in the same JAMA issue, two pediatricians, Dr. Sean O’Leary of the University of Colorado Anschutz Medical Campus and Dr. Yvonne Maldonado of the Stanford University School of Medicine, wrote that the recent findings reassured that the US childhood vaccine schedule was safe regarding the increased risk of non-targeted infections.

Despite the promising and reassuring findings, more efforts are needed to strengthen the public’s confidence in vaccines. The authors wrote, “Simply providing scientific information and assuming parents will make the decision to vaccinate is not enough. 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.”

A Danish study using national registry data for children born between 1990 and 2001 examined the association between seven childhood vaccinations and non-targeted infectious diseases in children. Despite using a different population, study period, study design and method of defining the exposure, this Danish study arrived at the same conclusion with the current U.S. study: Multiple vaccine exposures do not damage the immune system and make kids more vulnerable to diseases that are not covered by the immunizations.

Melvin Sanicas is an infectious disease physician.

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