HHS To Remove Little-Used Thimerosal From All Influenza Vaccines

Department of Homeland Security (DHS) Secretary Kristi Noem tours the National Biodefense Analysis and Countermeasures Cetner with Health and Human Services Secretary Robert F. Kennedy, Jr. and U.S. Senator Rand Paul on Fort Detrick, Maryland, June 16, 2025. (DHS photo by Tia Dufour)

Flickr/DHS/Tia Dufour

The decision follows last month’s vote of the CDC’s revamped vaccine advisory committee. Thimerosal, mostly removed from vaccines decades ago, has long been a target of anti-vaccine advocates for unfounded links to autism and adverse health outcomes.

The Department of Health and Human Services has adopted the CDC’s vaccine committee recommendation to remove the preservative thimerosal from all U.S. influenza vaccines.

The move, announced Wednesday, comes after the Advisory Committee for Immunization Practices (ACIP) on June 26 voted unanimously to remove thimerosal from all influenza vaccines. Thimerosal is present in about 4% of influenza vaccines in 2025. It was mostly removed from vaccines after a 1999 FDA order to do so, following years of concern from anti-vaccine critics who called its safety into question.

According to the CDC, only three products—two from Seqirus and one from Sanofi Pasteur—contain thimerosal. HHS’ statement said that manufacturers could replace thimerosal-containing vaccines without interrupting vaccine supplies.

Thimerosal is used in multi-dose vials of vaccines to prevent bacterial and fungal growth. This makes vaccinating large groups, particularly in remote and rural areas, significantly easier since an entire area can be immunized from a single vial using fresh needles.

Critics of its use point to the presence of ethylmercury, which they compare to the dangers of ingesting methylmercury, a known human poison. Those against thimerosal also suggest thimoersal-containing vaccines have some link to incidence of autism.

“After more than two decades of delay, this action fulfills a long-overdue promise to protect our most vulnerable populations from unnecessary mercury exposure,” HHS Secretary Robert F. Kennedy Jr. said in a statement.

According to the CDC, however, thimerosal and ethylmercury are safe, cleared from the body rapidly and have no link to autism. “There is a robust body of peer-reviewed, scientific studies . . . that support the safety of thimerosal-containing vaccines. The scientific evidence collected over the past 20+ years does not show any evidence of harm, including serious neurodevelopmental disorders, from use of thimerosal in vaccines,” reports the CDC.

Without thimerosal, manufacturers must produce much more single-dose vaccine products, though other types of preservatives are also available.

“Injecting any amount of mercury into children when safe, mercury-free alternatives exist defies common sense and public health responsibility,” Kennedy said. “Today, we put safety first.”

On the other hand, some raised the potential that banning it could reduce vaccine access. At last month’s meeting, ACIP members seemed unconvinced and concerned about the ramifications of the removal.

“My concern is that by insisting that vaccine doses not contain thimerosal, that might lower vaccine access,” ACIP member Cody Meissner said after the vote. “The risk from the flu is so much higher than [from] thimerosal, I would hate for someone not to receive the vaccine because it does contain thimerosal.”

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