A sweeping analysis of health data from more than 1.2 million children in Denmark born over a 24-year period found no link between the small amounts of aluminum in vaccines and a wide range of health conditions—including asthma, allergies, eczema, autism, and attention deficit-hyperactivity disorder (ADHD).

The finding, published in the Annals of Internal Medicine, firmly squashes a persistent anti-vaccine talking point that can give vaccine-hesitant parents pause.

Small amounts of aluminum salts have been added to vaccines for decades as adjuvants, that is, components of the vaccine that help drum up protective immune responses against a target germ. Aluminum adjuvants can be found in a variety of vaccines, including those against diphtheria, tetanus, and pertussis, Haemophilus influenzae type b (Hib), and hepatitis A and B.

Despite decades of use worldwide and no clear link to harms, concern about aluminum and cumulative exposures continually resurfaces—largely thanks to anti-vaccine advocates who fearmonger about the element. A leader of such voices is Robert F. Kennedy Jr, the current US health secretary and an ardent anti-vaccine advocate.

In a June 2024 interview with podcaster Joe Rogan, Kennedy falsely claimed that aluminum is “extremely neurotoxic” and “give[s] you allergies.” The podcast has racked up nearly 2 million views on YouTube. Likewise, Children’s Health Defense, the rabid anti-vaccine organization Kennedy created in 2018, has also made wild claims about the safety of aluminum adjuvants. That includes linking it to autism, despite that many high-quality scientific studies have found no link between any vaccines and autism.

While anti-vaccine advocates like Kennedy routinely dismiss and attack the plethora of studies that do not support their dangerous claims, the new study should reassure any hesitant parents.

Clear data, unclear future

For the study, lead author Niklas Worm Andersson, of the Statens Serum Institut in Copenhagen, and colleagues tapped into Denmark’s national registry to analyze medical records of over 1.2 million children born in the country between 1997 and 2018. During that time, new vaccines were introduced and recommendations shifted, creating variation in how many aluminum-containing vaccines children received.