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In the largest study of its kind, researchers examined aluminum exposure from vaccines in 1.2 million children, and found no increased risk of autism, asthma, or autoimmune disease.

Study: Aluminum-Adsorbed Vaccines and Chronic Diseases in Childhood: A Nationwide Cohort Study. Image credit: Drazen Zigic/Shutterstock.com

Aluminum is an effective and common adjuvant used in multiple non-live childhood vaccines. Some recent studies have raised concerns about its potential to cause chronic childhood diseases, such as atopic, autoimmune, or neurodevelopmental disorders. A recent paper in Annals of Internal Medicine does not show an association with such disorders, unless those of extreme rarity exist.

Introduction

Aluminum adsorbs vaccine antigens and is hence used as a vaccine adjuvant for several childhood vaccines, including diphtheria, tetanus, pertussis, Haemophilus influenzae type b (Hib), pneumococcal conjugate vaccine (PCV), and hepatitis A and B vaccines. These have been in worldwide use for multiple decades without safety issues being flagged.

However, some animal studies suggested that aluminum might potentially cause neurotoxicity, autoimmune, or atopic disease. Notably, there is no human data to refute or confirm these findings. Most have come from small observational studies. The current study aimed to use population-wide, large-scale data to explore the possibility of such associations.

All children living in Denmark are offered childhood vaccines free of charge. Uptake during the first two years stood at 94% to 97% in 2023. The aluminum content of the vaccines has changed over time, as has the vaccination schedule. For instance, PCV was incorporated in 2007, while others were substituted due to shortages or newer formulations.

The result is that birth cohorts have received different doses of aluminum, with varying cumulative dosages unrelated to individual characteristics. These systematically imposed differences provided a quasi-experimental setup for the analysis, helping to limit bias and confounding.

The cohort study drew on nationwide Danish registry data to examine potential associations between childhood vaccinations and chronic neurodevelopmental, autoimmune, or atopic disease. It included over 1.2 million children born there between 1997 and 2018, with outcomes assessed until they reached five years of age. 

The exposure was the cumulative amount of aluminum obtained via vaccination during these two years. The outcomes included incidences of 50 chronic diseases belonging to:

• Neurodevelopmental disorders – autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD)
• Autoimmune – skin, hormonal, blood-related, digestive, or joint illness
• Allergic – asthma, eczema, rhinoconjunctivitis, and allergy

Study outcomes

The median exposure was 3 mg, ranging from 0 to 4.5 mg. As expected, the birth year was linked to cumulative aluminum dosage by two years.

Only about 1% of children did not receive any aluminum-adsorbed vaccines by two years of age. Children who received up to 1.5 mg aluminum were more likely to have a lower socioeconomic level and to meet doctors less often. Those who received >3 mg aluminum were more likely to be born to mothers with mental illness and diabetes.

Among the outcomes, 20 autoimmune disorders registered fewer than 20 cases and were excluded from separate analysis. The incidence of all autoimmune diseases varied between 0.8 and 50.5 cases per 1,00,000 person-years. There was no increase in risk for autoimmune disease as a whole, nor for individual conditions.

For atopic conditions, asthma incidence did not exceed that in the unvaccinated group. No increased risk was found for atopic dermatitis or allergic rhinitis, and all atopic conditions failed to show an association with aluminum exposure. Similar trends were observed with neurodevelopmental disorders, which occurred among nearly 6,000 children under five years of age. There was no risk increase, and hazard ratios suggested a modest reduction in risk, by 7% for ASD and 10% for ADHD per 1 mg aluminum increase, although causality cannot be inferred.

Thus, the researchers found no association between outcome and cumulative aluminum exposure. The risk of new-onset disorders in any of the three groups did not exceed baseline. The upper bounds of the 95% confidence intervals were incompatible with small to moderate increases in risk for most outcomes. Where bounds exceeded 30%, outcomes were extremely rare, at fewer than 15 cases per 1 million person-years.

These findings conflict with prior cohort studies that suggested a slight increase in atopic disease risk per 1 mg aluminum exposure via vaccination before the age of two years. However, these studies did not account for known confounding factors, like maternal smoking or a tendency to atopic symptoms. In addition, only around 60% of children in those studies were fully vaccinated, raising the risk of residual confounding.

The current study adjusted for a comprehensive range of confounders, including maternal health conditions, smoking during pregnancy, parity, and socioeconomic status. Prior research suggests aluminum levels in vaccinated infants are below the minimal risk level.

Conclusion

These findings do not suggest that aluminum-adjuvant vaccines increase the child’s risk for most autoimmune, atopic, or neurodevelopmental disorders. For most outcomes, the results were inconsistent with even modest risk increases. However, small relative increases for very rare disorders could not be ruled out due to statistical limitations.

These results support the overall safety of aluminum-adsorbed vaccines in early childhood as part of national immunization programs.

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