The United States will no longer distribute influenza vaccines containing thimerosal, a mercury-based preservative, marking a dramatic shift in federal vaccine policy under Health Secretary Robert F. Kennedy Jr.

The move follows a recommendation from a vaccine advisory panel, whose members were appointed by Kennedy, to phase out thimerosal-containing flu shots. Though the additive has long been deemed safe by health authorities, the panel voted last month in favour of thimerosal-free vaccines “as a precautionary and modernising step,” according to Kennedy.

Thimerosal has been at the centre of controversy for decades. Anti-vaccine activists have blamed it, without scientific basis, for causing autism and other developmental disorders. Kennedy himself authored a 2014 book calling for “the immediate removal of mercury from vaccines.”

Currently, about 5% of flu shots in the US use multi-dose vials containing thimerosal, which was largely phased out beginning in the early 2000s. The FDA states on its website that thimerosal was never shown to be dangerous in vaccines, and its removal was “a precautionary measure to reduce overall mercury exposure in infants.”

Some experts on the advisory panel dissented. One panellist noted, “The risk of people avoiding the flu vaccine because they fear thimerosal may actually outweigh any risk from the ingredient itself.”

Despite the disagreement, Kennedy accepted the panel’s recommendation. In an unusual move, the decision was formalized without sign-off from the CDC director, a role currently unfilled as President Trump’s nominee, Susan Monarez, awaits Senate confirmation.

The Health and Human Services Department (HHS) assured the public that the policy shift will not disrupt flu vaccine supply. Vaccine manufacturers have confirmed that they have the capacity to replace multi-dose vials containing the preservative.

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