Do any vaccines still contain mercury-based preservatives today?
Executive summary
A mercury-containing preservative called thimerosal (also spelled thiomersal) has been removed from most routine childhood vaccines in the U.S. since the early 2000s, but until recently it remained in a subset of multi-dose influenza vaccine formulations and in some vaccines used in low-resource settings; in mid‑2025 U.S. health authorities moved to eliminate it from all influenza vaccines distributed domestically [1] [2] [3] [4].
1. What “mercury in vaccines” actually means: a chemical and a history
Thimerosal is an organomercury compound that metabolizes to ethylmercury and has been used since the 1930s as a preservative in multi‑dose vials to prevent bacterial and fungal contamination; it is chemically distinct from methylmercury found in some fish and was removed from most childhood vaccine formulations beginning after a 1999 precautionary recommendation [5] [3] [6].
2. The modern U.S. landscape before the 2025 policy change
By the 2000s nearly all routinely recommended childhood vaccines for children under six were thimerosal‑free or contained only trace amounts left from manufacturing, but certain inactivated influenza vaccines packaged in multi‑dose vials continued to contain thimerosal because those presentations require a preservative for repeated punctures [7] [2] [8].
3. The 2025 debate and policy shift that matters now
A renewed policy debate in 2025 culminated in the Advisory Committee on Immunization Practices voting to stop recommending flu vaccines containing thimerosal and the HHS secretary formally adopting a recommendation to remove thimerosal from all U.S. influenza vaccines, directing that children, pregnant women and adults receive single‑dose influenza vaccines free of mercury—marking a formal national policy change [9] [4].
4. Global context and who still uses thimerosal
While the U.S. has driven down thimerosal use and in 2025 moved to eliminate it from domestic influenza vaccine lots, public‑health bodies and vaccine producers have long warned that multi‑dose vials without preservatives present cost and access challenges in low‑resource settings; internationally, some developing‑country vaccination programs have continued using thimerosal‑containing multi‑dose vials because of logistical and economic constraints [3] [5].
5. Safety, science and the politics shaping public perception
Extensive epidemiologic studies and reviews have not found a causal link between thimerosal in vaccines and autism or neurodevelopmental disorders—and many professional bodies emphasize that the precautionary removal from routine infant vaccines was policy‑driven rather than evidence of harm—but the ingredient remains a flashpoint for vaccine skeptics and political actors, and recent ACIP discussion highlighted both scientific interpretations and precautionary impulses that motivated policy change [1] [6] [9] [10].
6. Bottom line answer to the question
As of the post‑2025 U.S. policy action, no routine U.S. childhood vaccines contain thimerosal as a preservative and HHS has moved to remove thimerosal from all influenza vaccines distributed domestically, meaning that — in the United States — vaccines containing mercury‑based preservatives are effectively being phased out and are no longer part of the routine supply [1] [4]. Internationally, however, some multi‑dose formulations containing thimerosal have continued in use where single‑dose options are impractical or too costly, so the global picture is more mixed [3] [5].