When anti-vaccine activists and others argue that the immunizations used to protect children from infectious diseases are risky, they often point to aluminum salts, a product added to many childhood vaccines to increase their effectiveness.
A new large study from Denmark directly counters those claims. After mining the vaccination and medical records of more than 1.2 million children over a 24-year period, researchers could see no evidence that exposure to aluminum in vaccines led to a statistically significant increase in a child’s risk of developing any of a wide variety of conditions that can be diagnosed in childhood, including asthma and autism.
None of the 50 conditions the group looked at — broadly categorized as relating to autoimmune diseases, allergy, and neurodevelopmental disorders — occurred at statistically higher levels than would be expected, ruling out moderate or substantially increased risk from exposure to aluminum in vaccines, a finding senior author Anders Hviid described as “quite striking.”
“We can exclude meaningful increases with a large degree of certainty for many of these outcomes,” Hviid, who heads the department of epidemiology research at the Statens Serum Institut, Denmark’s public health agency, told STAT in an interview.
“We should not be concerned about aluminum used as an adjuvant in childhood vaccines. I think that’s the core message.”
Hviid and his co-authors said that while there wasn’t a statistically significant increase seen for any of the conditions they studied, they could not rule out the possibility of a small increased risk for some very rare conditions. “So that tells us that clearly that there’s not an epidemic of chronic diseases in childhood’’ associated with aluminum in vaccines, he said.
The article was published Monday in the journal Annals of Internal Medicine.
Other experts agreed with Hviid’s take on the findings.
“I was very encouraged by the data, particularly for asthma as I know vaccine hesitancy groups are concerned by this,” said Anna Durbin, director of the Center for Immunization Research at Johns Hopkins Bloomberg School of Public Health.
Matthew Daley and Jason Glanz, two authors of an earlier U.S.-based study that suggested aluminum in childhood vaccines might be tied to an increased risk of developing asthma before age 5, also welcomed the publication. Daley and Glanz, both of whom work at Kaiser Permanente Colorado’s Institute for Health Research, both described the study as well done.
On the issue of asthma risk in particular, Daley said this new study should provide reassurance to parents that vaccinating their children according to the recommended schedule should not increase their risk of developing asthma.
“As a practicing pediatrician, I find that reassuring, and my patients and other clinicians I work with should find that reassuring,” said Daley, who noted that even after publishing his study about the possible association between aluminum in vaccines and asthma, he continued to urge parents to vaccinate their children, because he felt the benefits of vaccination were greater than the small possible risk his work identified.
Aluminum salts are added to some pediatric vaccines to improve the immune response they stimulate. They are used in inactivated vaccines — vaccines made from killed viruses or bacteria — and protein-based vaccines. Vaccines that use live but weakened viruses, such as the measles, mumps, and rubella vaccine, do not contain aluminum, nor do vaccines made using messenger RNA, like several of the Covid-19 vaccines.
Aluminum salts have been used for more than 70 years, and there is a large body of evidence supporting their safety and effectiveness. But they have attracted the attention of opponents of vaccines, who argue they may overstimulate immune systems. The amount of aluminum that children are exposed to through vaccines is well below accepted safe limits.
Daley and his co-authors undertook their study after a 2013 report on vaccine safety from the Institute of Medicine — which has since been renamed the National Academy of Medicine — urged additional research of whether there might be a link between exposure to aluminum in vaccines and the development of asthma. After their results were published in the journal Academic Pediatrics in 2023, Hviid and his colleagues in Denmark were inspired to take another look.
“I feel a sense of gratitude that they undertook this study,” Daley said.
Investigating the safety of aluminum in vaccines is challenging because aluminum is ubiquitous — it’s the third-most abundant element on the planet, Glanz said. Humans encounter it daily, in food, for instance. It is even found in breast milk.
Hviid and colleagues from the Statens Serum Institut and from the University of Copenhagen used Denmark’s nationwide health care registries to compile a cohort of 1.2 million children born between 1997 and 2018, checking for diagnoses for 50 conditions. They examined the records of the children out to 5 years of age.
Because the number of vaccines given in early childhood changed over the 24-year study period, the researchers were able to determine whether rates of any of these conditions changed as the amount of aluminum children received via vaccinations increased when new vaccines were added to the schedule.
That they didn’t see differences among children who received more vaccines in early childhood is a strength of the study, Daley said. That’s because if something causes a biological effect, receiving more of the substance should exacerbate the effect. It’s a phenomenon referred to as a dose response.
“They don’t see any dose response there at all. And their study was set up to see a dose response if one was there,” he said.
Daley noted a few caveats in interpreting the results, pointing out that the vaccine schedule in Denmark is slightly different from the one used in the United States.
“They immunize at 3 months, 5 months, 12 months. We immunize at 2 months, 4 months, 6 months, 12 months. I would be surprised that that slight difference between 2 and 3 months would make a big difference. But it is important to acknowledge that there is a difference we should keep in mind,” he said.
Likewise, this isn’t a randomized controlled trial; researchers were not comparing children who received no aluminum-containing vaccines to children who did get shots containing aluminum. Such a study would not be ethical to conduct because withholding vaccines from some children would put them at risk of serious illnesses.
But the size of this study and the clear-cut nature of the results underscores the safety of these critical vaccines, Hviid said.
“These aluminum-adjuvanted vaccines are really important for our immunization programs. Not just in Denmark, not just in the U.S., but globally,” he said. “We don’t have any replacements for these vaccines with other adjuvants. So if you take them away, children are going to die.”
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