It’s natural for people to have questions about vaccines and how each ingredient plays a role. Each ingredient included in a vaccine plays a necessary role in ensuring a vaccine’s safety, quality or effectiveness. All ingredients in vaccines are evaluated during the FDA vaccine review process and must meet rigorous safety standards.
Two ingredients that often come up in conversations about vaccine safety are aluminum and thimerosal. Here’s what you need to know:
Is aluminum used in vaccines and why?
Some vaccines contain small amounts of aluminum salts, which are used as adjuvants—ingredients that help strengthen the body’s immune response to a vaccine. Adjuvants have been used safely in vaccines for decades and allow vaccines to be more effective with fewer doses.
Aluminum is a naturally occurring element and is present in many everyday sources, including drinking water and a wide range of food. The amount of aluminum in vaccines is very small —far less than what people encounter through their diet or environment.
Is aluminum in vaccines safe?
The small amount of aluminum used in vaccines is well within safe limits established by independent public health authorities. As one expert source notes, “while infants receive about 4.4 milligrams of aluminum in the first six months of life from vaccines, they receive more than that in their diet. Breast-fed infants ingest about 7 milligrams, formula-fed infants ingest about 38 milligrams, and infants who are fed soy formula ingest almost 117 milligrams of aluminum during the first six months of life.”
Studies have shown that the body efficiently processes and eliminates aluminum from vaccines, and extensive clinical trial data and decades of real-world use have not identified any health risk associated with aluminum adjuvants. Recent large-scale studies — including a 2023 analysis of over 450,000 children—have found no associations between aluminum and chronic conditions like asthma.
What is thimerosal, and is it used in vaccines?
Thimerosal is a preservative that has been used in some vaccines to prevent contamination by bacteria or fungi. It contains ethylmercury, which is quickly processed and eliminated by the body and is different from methylmercury, the form associated with environmental exposure and toxicity.
As a precautionary measure, in July 1999, the U.S. Public Health Service, the American Academy of Pediatrics and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines. Since 2001, all vaccines routinely recommended for children six years of age and younger are thimerosal-free, except for some formulations of inactivated influenza vaccine. The decision to reduce its use was made to support public confidence—not because of any identified safety risks.
Does thimerosal pose any health risks or increase risk for autism?
No. Numerous large scale studies and reviews over decades have consistently found no link between vaccines containing thimerosal and autism or other long-term health issues.
It’s understandable that parents may have questions about the causes of autism, but research has shown that autism arises from various genetic and environmental factors, and diagnoses have risen in part because of increased screening. Based on decades of extensive research, no link has been found between vaccines or vaccine ingredients and autism. Further research is needed to get a clearer understanding of autism’s root causes. Understanding root causes can improve how autism is identified, leading to earlier and more accurate diagnoses.
Learn more at PhRMA.org/Vaccines.
Mike Ybarra
Michael Ybarra, M.D., is an emergency physician and Chief Medical Officer at PhRMA. He also serves as Senior Vice President in Advocacy and Strategic Alliances. In these roles, he leads PhRMA’s stakeholder engagement and strategic partnerships on federal and international health policy issues. He is PhRMA’s liaison representative to the Advisory Committee on Immunization Practices and is the co-convener of PhRMA’s R&D Leadership Forum. Dr. Ybarra continues to see patients clinically in the emergency department at MedStar Georgetown University Hospital.
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Mike Ybarra