Results From Danish Study Find No Increased Risk From Aluminum-Containing Childhood Vaccines

Results from a comprehensive nationwide cohort study from Denmark, published online ahead of print in Annals of Internal Medicine, have found no evidence linking early childhood exposure to aluminum-containing vaccines with an increased risk of chronic autoimmune, allergic, or neurodevelopmental disorders. This important research comes amid ongoing public concerns about the safety of aluminum adjuvants, widely used to boost immune responses in nonlive childhood vaccines.

Aluminum salts have long been used as vaccine adjuvants, yet questions remain about whether their cumulative exposure could contribute to long-term health issues such as autoimmune diseases, allergies, or neurodevelopmental conditions such as autism spectrum disorder and attention-deficit/hyperactivity disorder. To address these concerns, researchers examined over 1.2 million Danish children born between 1997 and 2018 who were alive and residing in the country at the age of 2 years.

By linking detailed vaccination records, specifically aluminum content, with nationwide health registries, the study analyzed diagnoses of 50 chronic disorders across autoimmune, atopic/allergic, and neurodevelopmental categories. Cumulative aluminum exposure in the first 2 years of life was the main exposure variable to assess dose-related risk.

In our interview with Anders Peter Hviid, head of epidemiology research at Statens Serum Institute in Denmark and lead investigator of the study, he explained the strength of the data. "The validity of our study really comes from the data—the source data—the very unique situation that we have here in Denmark and the other Nordic countries. Every citizen in Denmark has their own unique ID [identification], the CPR [Civil Registration System] number, and this CPR number is used in all our registries, and we have many registries, and they are nationwide."

He added that Denmark’s universal and free health care system allows researchers to "follow the whole Danish population over time, over many years, with complete and detailed information on health care. For example, which vaccines the children have received, when they've received them, and what happens later on with respect to different diagnoses."

Given that this was an observational study, Hviid emphasized their approach to control for confounding factors: "We are always concerned about comparability between the 2 or more exposure groups that we look at. Again, having access to large different registries allows us to pull in information from these registries to enrich the analysis and try to take these differences into account. [It] could be something like socioeconomics."

The study results found no significant increase in risk for any of the 50 chronic disorders examined with higher cumulative aluminum exposure from vaccines. The adjusted HRs per 1-mg increase in aluminum dose were close to 1 for autoimmune disorders (HR, 0.98; 95% CI, 0.94-1.02) and allergic disorders (HR, 0.99; 95% CI, 0.98-1.01), indicating no meaningful association. For neurodevelopmental disorders, a slight decrease in risk was observed (HR, 0.93; 95% CI, 0.90-0.97). For most outcomes, the CIs excluded moderate- or large-risk increases.

When asked how these findings compare with previous research and what they mean for public health policy, especially in light of concerns raised by figures such as Robert F. Kennedy Jr, Hviid responded, "There's quite a lot of research that has actually looked at aluminum-containing vaccines, because many of our vaccines used today in the childhood immunization schedules do contain aluminum. And we do—and have done for many years—careful safety evaluations of these vaccines."

What distinguishes this study, he noted, is its ability to isolate the effects of the aluminum ingredient itself rather than comparing vaccinated children with unvaccinated children: "What's particular about our study is that we separate the effect of a vaccine from this ingredient. So the variation is in the amount of aluminum received through vaccination, and that is in contrast to what I talked about before—comparing vaccinated with unvaccinated children, where you're basically comparing the vaccine with the adjuvant to nothing at all. These studies are quite common, whereas our study is more rare—studies that are able to disentangle the impact of the aluminum adjuvant ingredient."

He further shared that their study was inspired by a 2023 US and British study by the Centers for Disease Control and Prevention (CDC) focused on asthma, results of which suggested a possible increased risk associated with aluminum.

"They found a signal—they found a slightly increased risk of asthma by 5 years of age associated with increasing amounts of aluminum received through vaccines. I was informed by CDC colleagues of this and asked if I could try to reproduce their results, and that's how it started. We did that and also presented these preliminary findings at an earlier AC meeting. Then we have expanded and built on top of that with a huge range of outcomes that we look at in this study." He emphasized that large epidemiological studies capable of isolating aluminum’s specific effect are relatively rare.

Hviid also revealed plans for future work within the existing cohort: "From our perspective, I think we have this large cohort, and we will be able to continue following up these children for these outcomes in higher age groups. We have also talked about looking into the possibility of trying to see if there's a link between aluminum adjuvant and cognitive issues."

He explained how Danish registries enable such investigations: "We have registries for everything. So that would be a wonderful way to use as a proxy for cognitive issues—to see if there's a link between aluminum adjuvant and cognitive issues. That would be a supplement to this current study, where we are focusing more on hard end points—end points resulting in a clinical diagnosis in the health care system."

Although the study’s scale and detailed registry data provide robust evidence, individual medical records were not reviewed. Hviid acknowledged this limitation, noting that "very small effects, especially for rare conditions, cannot be completely excluded."

Reference

Andersson NW, Bech Svalgaard I, Hoffmann SS, Hviid A. Aluminum-adsorbed vaccines and chronic diseases in childhood : a nationwide cohort study. Ann Intern Med. Published online July 15, 2025. doi:10.7326/ANNALS-25-00997