A little-used vaccine ingredient is unexpectedly back on the agenda for a key federal advisory panel, leaving many public health experts puzzled. The Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices (ACIP), an influential body shaping U.S. vaccine policy, is scheduled to vote on thimerosal, a preservative that has been largely phased out of most vaccines.
What is Thimerosal?
Thimerosal is a preservative introduced in the 1930s. Its primary purpose was to prevent potentially dangerous bacterial and fungal growth in multi-dose vaccine vials that are punctured multiple times to vaccinate many people. Chemically, thimerosal contains ethylmercury, a compound related to mercury but processed and eliminated from the body differently than the more harmful methylmercury found in some foods.
Despite scientific consensus on its safety, thimerosal became a focal point for vaccine skeptics who falsely claimed it contributed to autism. However, thimerosal has been removed from most childhood vaccines and significantly reduced in others over the past two decades, while autism rates have continued to rise, further disproving this unfounded link.
Why the Confusion Over the Vote?
The ACIP’s planned vote on thimerosal has raised eyebrows among many vaccine scientists and public health professionals. The main source of bewilderment is thimerosal’s limited use in current vaccines.
According to the CDC’s most recent data, approximately 94% of flu vaccines distributed in the U.S. during the latest season were either completely thimerosal-free or preservative-free. Thimerosal primarily remains in a small percentage of flu vaccine formulations, specifically those provided in multi-dose vials.
Dr. Jason Goldman, president of the American College of Physicians and a liaison member to ACIP, expressed his surprise, stating the agenda item “just isn’t making sense.” He highlighted that given its minimal presence, the renewed focus feels hard to justify.
Safety is Proven, Link to Autism Debunked
Leading medical experts unequivocally state that thimerosal is safe and does not cause autism. Dr. Goldman and Dr. Mark Abdelmalek, an ABC News medical contributor with extensive experience in vaccine policy, both reinforced the scientific consensus:
“Autism is not caused by vaccines,” said Dr. Goldman, emphasizing this has been proven “time and time again.”
Dr. Abdelmalek added, “Thimerosal has been proven safe and there is no evidence to suggest thimerosal causes autism.”
The Critical Role of Multi-Dose Vials
While thimerosal is rare in single-dose vaccines common in the U.S., it (or another preservative) is essential for the safety of multi-dose vials. These vials are crucial for efficiency, requiring less storage space and allowing for faster vaccination processes. They play a vital role in:
Global vaccination programs
Lower-resource clinics in the U.S.
- Remote or far-away locations
- abcnews.go.com
Experts caution that removing thimerosal from these vials without replacing it could compromise vaccine safety by allowing bacterial or fungal contamination after the vial is opened. The idea of eliminating all preservatives from vaccines, particularly multi-dose ones, is considered “unrealistic or safe for that matter,” according to Dr. Abdelmalek.
Political Context and Expert Concerns
The unexpected inclusion of thimerosal on the ACIP agenda is occurring under unusual circumstances. With no confirmed CDC director in place, Health and Human Services Secretary Robert F. Kennedy Jr., a noted vaccine skeptic who has promoted false claims about thimerosal and autism, has taken a leading role in overseeing the agency. This includes appointing members to the ACIP panel and chairing public meetings.
Concerns have also been raised about the participation of individuals associated with anti-vaccine groups. Lyn Redwood, former president of Children’s Health Defense (an organization founded by RFK Jr.), is slated to present before the ACIP vote on thimerosal.
Experts worry that revisiting the thimerosal issue, despite the overwhelming scientific evidence of its safety and limited use, could inadvertently reinforce the false narrative that it is unsafe. Dr. Goldman questioned the motives behind reintroducing the topic, speculating it could be a tactic to “delay, delay, delay” or potentially “further sow doubt about vaccines in general,” especially given the influence of individuals skeptical of vaccines on the panel and leadership.
While an ACIP vote to remove thimerosal from the remaining flu vaccine supply might signal a policy stance, it would have little practical impact on the vast majority of Americans who already receive preservative-free single-dose shots. The true impact, experts suggest, might be less about public health policy and more about generating controversy and reinforcing unfounded fears about vaccine safety.
