Mercury Out: RFK Jr. Makes Good on Vaccine Promise

Health and Human Services Secretary Robert F. Kennedy Jr. put his signature on a document Wednesday that vaccine critics have been demanding for decades. After years of debate, false claims, and scientific studies clearing the ingredient in question, American flu shots will no longer contain thimerosal, a mercury-based preservative used since the 1930s.

Yet the move affects just 4 to 5 percent of flu vaccines currently distributed across the United States. Nearly all Americans already receive thimerosal-free shots delivered in single-dose prefilled syringes. Scientists say no evidence exists that the preservative causes harm. Medical experts warn the decision sends the wrong message to a public already skeptical of vaccines.

So why does this matter? Because Kennedy fired an entire federal vaccine advisory panel in June and replaced them with handpicked allies, some from the anti-vaccine movement. Because one of those allies presented information containing a link to a study that does not exist. Because Kennedy pulled a CDC presentation on thimerosal safety before the committee voted.

And because what happens in America reverberates globally, particularly in lower-income countries that rely heavily on multi-dose vaccine vials containing thimerosal.

What Changed on July 23

Kennedy formally adopted recommendations from the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices to eliminate thimerosal from all influenza vaccines distributed in the United States. ACIP voted 5-1 at its June meeting in Atlanta, with one member abstaining.

“After more than two decades of delay, this action fulfills a long-overdue promise to protect our most vulnerable populations from unnecessary mercury exposure,” Kennedy said in a statement. “Injecting any amount of mercury into children when safe, mercury-free alternatives exist defies common sense and public health responsibility.”

Multi-dose formulations of Sanofi’s Fluzone and two shots from biotech company CSL Seqirus will need reformulation. Manufacturers have confirmed they possess the capacity to replace these vials, according to HHS. Programs providing vaccines to uninsured and underinsured children will continue without interruption, the agency added.

Implementation could begin as early as the 2025-2026 flu season, though some vaccines have already shipped to pharmacies nationwide.

Understanding a Decades-Old Preservative

Thimerosal contains ethylmercury, which differs from methylmercury found in fish like tuna. Ethylmercury clears from the body faster than its counterpart, reducing any potential exposure time. A single flu vaccine contains about 25 micrograms of ethylmercury. For comparison, a three-ounce serving of canned tuna contains roughly 40 micrograms of methylmercury.

Drug manufacturers began using thimerosal in the 1930s to prevent bacterial and fungal contamination in multi-dose vials. Each time a needle punctures these vials to draw a dose, contamination risk increases. Single-dose vials and prefilled syringes eliminated the need for preservatives because they are used once and discarded.

Most childhood vaccines removed thimerosal in 2001 after a precautionary agreement between the U.S. Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers in 1999. At the time, these groups said any potential risk warranted removal as soon as possible, though evidence of actual harm remained absent.

During the 2024-2025 flu season, 96 percent of flu vaccines administered in America contained no thimerosal. Only multi-dose vials retained the preservative.

Kennedy’s Committee Overhaul

Kennedy gutted ACIP in June, dismissing all 17 members and claiming conflicts of interest. He appointed eight new members to replace them, including several known for vaccine skepticism. Vicky Pebsworth, research director at the National Vaccine Information Center and a vocal figure in the anti-vaccine movement, joined the panel. She has claimed vaccines caused her son’s autism, a connection debunked by extensive research.

Another Kennedy appointee later withdrew following a conflict of interest review.

ACIP heard a presentation from Lyn Redwood, president emerita of Children’s Health Defense, an anti-vaccine organization Kennedy founded and previously chaired. Redwood appeared as a “private citizen,” a departure from normal ACIP practices where career scientists typically present data.

Reuters discovered Redwood’s presentation materials, posted days before the meeting, included a link to a study that does not exist. She updated the presentation after this revelation.

During the meeting, ACIP members asked why CDC safety information about thimerosal had vanished from the agency’s website. Robert Malone, an ACIP member and vaccinologist involved in early mRNA vaccine research, said Kennedy’s office pulled the document because it lacked authorization.

Career CDC scientists who prepared a presentation laying out thimerosal’s safety record never delivered it. Kennedy’s office pulled that presentation as well.

Medical Experts Voice Concerns

Cody Meissner, a professor of pediatrics at Dartmouth Geisel School of Medicine, cast the lone no vote on all three thimerosal recommendations covering children, pregnant women, and adults. Meissner has served on both CDC and FDA vaccine advisory committees throughout his career.

“No study has ever indicated any harm from thimerosal,” Meissner told the committee, noting ACIP generally makes recommendations based on scientific evidence. He worried that expressing a preference for single-dose vials might prevent people from receiving doses from multi-dose formulations when those shots represent the only available option.

Meissner raised concerns about costs and access. Discouraging multi-dose vials could increase vaccination expenses and limit availability for some groups. He also worried about messaging to countries where multi-dose flu vaccine formulations remain more common.

Several non-voting ACIP liaison members spoke against the recommendation, asking for CDC scientists to weigh in. Some raised concerns about implications for pandemic flu vaccines, which typically become available initially in multi-dose formulations.

Most other committee members focused on theoretical risk and concerns about cumulative mercury exposure, despite scientific evidence showing ethylmercury clears the body rapidly.

Pebsworth abstained from all three votes, objecting to the wording of voting questions rather than the substance.

What Four Decades of Research Shows

More than 40 studies spanning several decades have examined thimerosal safety. None found links between the preservative and developmental delays, autism, or other neurological problems. Organizations including the World Health Organization, FDA, and CDC have reviewed this evidence and determined thimerosal poses no risk at levels used in vaccines.

Autism rates actually increased after thimerosal removal from childhood vaccines in 2001, suggesting no positive correlation between the two.

In 2025, the American Academy of Pediatrics issued a statement rejecting its initial 1999 caution about thimerosal. AAP now states that “extensive research proves that thimerosal is a safe ingredient in vaccines, and it does not cause neurological problems or autism.” Their statement adds that “banning vaccine ingredients without solid scientific reasons sets a dangerous precedent and makes children less safe.”

Kate O’Brien, WHO’s vaccine chief, told reporters in June that “there is no evidence of harm from the use of thimerosal. For some of the vaccine supply, this is a very important ingredient in order to assure that we have the doses needed to protect children from serious and life-threatening diseases.”

Scientists who criticized the 2001 removal said it sent mixed messages and provided talking points for anti-vaccine campaigns. Those predictions proved accurate. Anti-vaccine groups targeted thimerosal for years following its removal from childhood vaccines, despite autism rates climbing during the same period.

Global Health Implications

Kennedy’s statement urged international action. “With the U.S. now removing mercury from all vaccines, we urge global health authorities to follow this prudent example for the protection of children worldwide,” he said.

Public health experts worry about consequences for lower-income countries. These nations rely more heavily on multi-dose vials because they cost less than single-dose alternatives. Multi-dose vials require repeated puncturing, raising contamination risk without preservatives like thimerosal.

Removing thimerosal could force these countries to switch to more expensive single-dose formulations or accept higher contamination risks. Either option could reduce vaccination rates and increase disease burden in populations already vulnerable to infectious diseases.

WHO officials have expressed concern that U.S. policy changes could influence global practices despite different circumstances and needs in various countries.

Pharmacy Response

Pharmacists find themselves on the front lines of addressing patient concerns about vaccine ingredients. Adam James, a pharmacist, interviewed about the decision, emphasized the importance of transparency. Pharmacists can clarify that nearly every vaccine administered in pharmacies comes as a single-dose, prefilled syringe already free of thimerosal.

Most patients receiving flu shots at retail pharmacies, grocery stores, or clinics have been getting thimerosal-free vaccines for years without knowing it. Single-dose syringes dominate the American market because they’re convenient and eliminate contamination concerns.

Medical professionals can use this moment to discuss vaccine safety more broadly, countering misinformation from various sources. Building trust through honest conversation about ingredients, manufacturing processes, and safety monitoring helps combat growing vaccine hesitancy.

Kennedy Sets Sights on More Vaccines

HHS said other recommendations from ACIP’s June meeting remain under review. Kennedy has not yet signed off on those proposals.

ACIP Chair Martin Kulldorff announced plans to establish two new working groups, both addressing topics popular among vaccine critics. One will evaluate the cumulative effects of vaccines on the CDC’s recommended schedule for children and adolescents. Another will examine vaccines in use for more than seven years, likely including hepatitis B vaccination at birth.

Kulldorff also aired a proposed recommendation about measles, mumps, rubella, and varicella vaccines in young children. MMRV carries a slightly higher risk of febrile seizures when given as a first dose compared with separate MMR and varicella vaccines, particularly among younger children. Kulldorff suggested that if safe, equally effective alternatives exist, MMRV should not go to children younger than 47 months. ACIP will vote on this proposal at a future meeting.

Kennedy’s victory on thimerosal represents more than a policy change about a preservative used in a small fraction of flu vaccines. It demonstrates how political appointments to scientific advisory panels can shift federal health policy away from evidence-based medicine toward positions long championed by vaccine skeptics, despite decades of research showing no harm from the targeted ingredient.