A large, nationwide study in Denmark, spanning 1.2m children and 24 years of data, found no link between aluminium in childhood vaccines and autism, asthma, or chronic disorders, the findings coming as conversations about aluminium in vaccines rise to the forefront in the US.
The study found that cumulative aluminium exposure from vaccination during the first two years of life did not raise the risk of autism, asthma, or other chronic disorders, adjusted hazard ratios (HRs) per 1-mg increase in aluminium exposure being 0.93 (95% CI 0.90-0.97) for any neuro-developmental disorder, 0.98 (95% CI 0.94-1.02) for any autoimmune disorder, and 0.99 (95% CI 0.98-1.01) for any atopic or allergic disorder, reported Niklas Worm Andersson, MD, PhD, of the Statens Serum Institut in Copenhagen, and co-authors.
“Aluminium salts in the extremely small amounts present in some childhood vaccines are not associated with any increased risk of 50 health conditions in early childhood,” corroborated co-author Anders Hviid, MSc, DrMedSci, also of Statens Serum Institut, reports Medpage Today.
“Our results provide robust evidence supporting the safety of childhood vaccines,” Hviid said. “This is evidence that parents, clinicians and public health officials need to make the best choices for the health of our children.”
The findings, published in Annals of Internal Medicine, help close the evidence gap about aluminium-absorbed vaccines and adverse events, especially neurological disorders, the researchers said.
In the United States last month, HHS Secretary Robert F Kennedy Jr considered asking a key government vaccine advisory panel to examine vaccines with aluminium ingredients, presumably due to questions about the metal’s potential ties to chronic conditions.
Aluminium is the most abundant metal in the earth’s crust and is present in most foods and drinks. While infants receive about 4.4mg of aluminium during their first six months from vaccines, they receive more from their diet: breast-fed infants ingest about 7mg, formula-fed infants consume about 38mg, and infants fed soy formula get almost 117mg of aluminium in those first six months.
Aluminium salts have been added to vaccines since the 1930s.
“The adjuvant allows you to develop an immune response that is protective, which you wouldn’t otherwise have,” Paul Offit, MD, of Children’s Hospital of Philadelphia, told MedPage Today. “It allows for lesser quantities of the actual vaccine, and it allows for fewer doses.”
The Denmark study answers a lot of questions, added Offit, who wasn’t involved with the report. Its strength lies in the Danish national healthcare system, he pointed out.
“The access to data is much easier in that system than it is here (US), where data are more fragmented,” he said.
In 2022, an analysis of Vaccine Safety Datalink (VSD) records led by Matthew Daley, MD, of Kaiser Permanente Colorado, found a possible association between aluminium exposure from vaccines and persistent asthma in a cohort of children.
“While recognising the small effect sizes identified and the potential for unmeasured confounding, additional investigation of this hypothesis appears warranted,” Daley and colleagues wrote at the time.
The CDC did not change vaccine recommendations based on the lone VSD study but said that “further investigation is needed into this potential safety signal”.
The VSD study left several questions unanswered: “They didn’t control for breastfeeding, which is protective against asthma,” Offit said. “They didn’t control for environmental pollution, which increases the risk of asthma. Most importantly, they didn’t control for family history.”
The Denmark study aimed to answer these questions, with preliminary results presented to the CDC’s Advisory Committee on Immunisation Practices in 2023.
Varying
Andersson and colleagues studied 1 224 176 children born in Denmark between 1997 and 2018, during which vaccines with varying aluminium content were introduced.
Diphtheria-tetanus-pertussis, Haemophilus influenzae type B, pneumococcal conjugate vaccine, inactivated poliovirus, and hepatitis A and B vaccines were included.
The researchers used nationwide health registries to determine the cumulative aluminium exposure from vaccines administered to each child before two-years-old, and to provide clinical data on the children until 2020 or until they reached five-years-old, died, or were lost to follow-up.
Study authors sought to investigate the incidence of 50 chronic diseases in particular, including 36 autoimmune, nine atopic or allergic, and five neurodevelopmental disorders. Among these 50 conditions were some very rare diseases and some more typically diagnosed after five years of age.
The researchers used regression models to estimate adjusted HRs when children received one additional mg of aluminium in vaccines by age two compared with children who received 1mg less.
For autism spectrum disorder, the HR per 1mg increase in cumulative aluminium exposure from childhood vaccination was 0.93 (95% CI 0.89-0.97), and for attention-deficit/hyperactivity disorder, it was 0.90 (95% CI 0.84-0.96). For asthma, the HR was 0.96 (95% CI 0.94-0.98).
For most individual outcomes, findings were inconsistent with moderate-to-large relative risk increases, though small relative effects for some rare disorders could not be excluded. “Our findings do not suggest an association, but these are rarer conditions, so the statistical precision in our results is lower,” Hviid said.
The analysis had several limitations, the researchers acknowledged. Because the study relied on data from routine clinical practice, exposure was not random. The researchers adjusted findings for a wide range of covariates including socioeconomic status, but residual confounding still may have influenced results.
Study details
Aluminium-Absorbed Vaccines and Chronic Diseases in Childhood: Nationwide Cohort Study
Niklas Worm Andersson, Ingrid Bech Svalgaard, Stine Skovbo Hoffmann, Anders Hviid.
Published in the Annals of Internal Medicine on 15 July 2025
Abstract
Background
Aluminium is used as an adjuvant in non-live vaccines administered in early childhood. Concerns persist about potential associations between vaccination with aluminium-absorbed vaccines and increased risk for chronic autoimmunity, atopy or allergy, and neuro-developmental disorders. Large-scale safety data remain limited.
Objective
To assess the association between cumulative aluminium exposure from early childhood vaccination and risk for autoimmune, atopic or allergic, and neuro-developmental disorders.
Design
A cohort study linking nationwide registry data on childhood vaccinations, outcome diagnoses, and potential confounders, leveraging the variations in the aluminium content of childhood vaccines over time.
Setting
Denmark, 1997 to 2020.
Participants
A total of 1 224 176 children born in Denmark between 1997 and 2018 who were living in the country at two years old.
Intervention
Cumulative aluminium amount received (per 1-mg increase) through vaccination during the first two years of life.
Measurements
Incident events of 50 chronic disorders, including autoimmune (dermatologic, endocrinologic, haematologic, gastrointestinal, and rheumatic), atopic or allergic (asthma, atopic dermatitis, rhinoconjunctivitis, and allergy), and neuro-developmental (autism spectrum disorder and attention deficit–hyperactivity disorder).
Results
Cumulative aluminium exposure from vaccination during the first two years of life was not associated with increased rates of any of the 50 disorders assessed. For groups of combined outcomes, adjusted hazard ratios per 1-mg increase in aluminium exposure were 0.98 (95% CI, 0.94 to 1.02) for any autoimmune disorder, 0.99 (CI, 0.98 to 1.01) for any atopic or allergic disorder, and 0.93 (CI, 0.90 to 0.97) for any neuro-developmental disorder. For most individually analysed outcomes, the upper bounds of the 95% CIs were incompatible with relative increases greater than 10% or 30%.
Limitation
Individual medical records were not reviewed.
Conclusion
This nationwide cohort study did not find evidence supporting an increased risk for autoimmune, atopic or allergic, or neuro-developmental disorders associated with early childhood exposure to aluminium-adsorbed vaccines. For most outcomes, the findings were inconsistent with moderate to large relative increases in risk, although small relative effects, particularly for some rarer disorders, could not be statistically excluded.
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