The Department of Health and Human Services on Wednesday said it will officially remove the mercury-based preservative thimerosal from all flu shots distributed in the U.S. – even though there is no evidence of harm from the ingredient. 

While few jabs still contain thimerosal, the move eliminates a vaccine option for Americans and is a win for the anti-vaccine movement, which has long targeted the ingredient.

HHS Secretary Robert F. Kennedy Jr. formally adopted a June recommendation from a key government vaccine panel, called the Advisory Committee on Immunization Practices, or ACIP, against influenza shots containing thimerosal. Earlier that month, Kennedy gutted that panel and restacked it with new members, including some widely known anti-vaccine activists. 

The decision affects roughly 4% to 5% of the U.S. flu vaccine supply. That includes some multi-dose forms of Sanofi‘s Fluzone and two shots from biotech company CSL Seqirus. The rest of the nation’s flu shots were thimerosal-free during the last season of the virus, according to CDC data.

Vaccine manufacturers have confirmed that they have the capacity to replace multi-dose vials containing mercury, HHS said. That will ensure that the flu vaccine for adults and a government program that provides shots to uninsured and underinsured children won’t be interrupted, the agency added. 

Still, health experts have said that eliminating thimerosal-containing flu shots as an option for Americans could lead to fewer people receiving jabs.

The move also reinforces longstanding, unfounded fears that the substance can lead to developmental disabilities, such as autism. Kennedy’s vaccine skepticism comes full circle with ACIP’s vote: A decade before stepping into his current role, he published a book that called for the removal of thimerosal from shots and linked it to developmental disorders.

“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 release, urging global health authorities to follow suit. 

More than 40 studies over several decades have found no link between thimerosal and developmental delays. Thimerosal has been widely used for decades as a preservative to prevent the growth of harmful bacteria in several medicines and vaccines with multiple doses.

HHS said other recommendations from the panel’s meeting in June are still under review.