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Which inactivated influenza vaccines available in 2025 contained thimerosal and which formulations were thimerosal-free?
Executive summary
Federal guidance and public reporting for the 2025–26 U.S. influenza season state that most influenza vaccine supply is thimerosal-free and that ACIP recommended—and HHS adopted—policies favoring single‑dose, thimerosal‑free influenza formulations; CDC projected most 2025–26 supply would not contain thimerosal [1], and ACIP/HHS moved to remove thimerosal from U.S. flu vaccines [2] [3]. At the same time, federal agencies (FDA, CDC) note that multi‑dose vials historically have contained thimerosal as a preservative and remain an option globally [4] [5].
1. What regulators said for 2025–26: a policy pivot toward thimerosal‑free flu shots
In mid‑2025 the Advisory Committee on Immunization Practices (ACIP) recommended that children ≤18, pregnant women and adults receive only single‑dose influenza vaccines free of thimerosal as a preservative, a recommendation that was included in the 2025–26 ACIP guidance [2]; Health and Human Services then adopted that recommendation, announcing removal of thimerosal from all U.S. influenza vaccines as federal policy [3].
2. How supply and formulations were described by CDC and FDA
CDC reported manufacturers projected up to 154 million doses for 2025–26 and stated “most of the projected influenza vaccine supply produced this influenza season does not contain thimerosal” and that multi‑dose vials with thimerosal accounted for a small share and were not recommended [1]. FDA materials also note that FDA‑approved seasonal influenza vaccines are available in single‑dose presentations that do not contain thimerosal as a preservative for all age groups [5].
3. Which vaccine presentations historically contained thimerosal
Public health agencies explain that thimerosal — an ethyl‑mercury preservative — has been used primarily in multi‑dose vials (MDVs) of influenza vaccine to prevent contamination; most single‑dose vials and prefilled syringes do not contain a preservative [4] [5]. Older reviews and summaries likewise document that the remaining notable source of non‑trace thimerosal exposure in vaccine schedules historically has been certain inactivated influenza MDVs [6].
4. Were any named 2025 vaccine products explicitly listed as thimerosal‑containing or thimerosal‑free in these sources?
Available sources do not provide a product‑by‑product list naming which specific manufacturer formulations in 2025 contained thimerosal versus which were thimerosal‑free. CDC and FDA state the general presentation rule—multi‑dose vials may contain thimerosal; single‑dose presentations and prefilled syringes generally do not—but do not enumerate every marketed product’s preservative status in the cited pages [4] [5] [1].
5. How common thimerosal‑containing flu shots were before the 2025 policy change
Analyses cited in reporting and health‑system data show that thimerosal‑containing influenza vaccines were already rare in U.S. practice: one dataset found 96% of administered influenza vaccines in the 2024–25 season did not contain thimerosal, and CDC said single‑dose, thimerosal‑free vaccines previously made up the majority of supply [7] [1].
6. Competing perspectives and the politics behind the recommendation
Medical authorities including FDA and CDC emphasise a robust body of scientific evidence supporting the safety of thimerosal at vaccine doses [5] [8]. Reporting and professional groups such as the American Academy of Pediatrics described the ACIP discussion as influenced by debunked studies and misinformation; AAP voiced concerns about the evidence base for the recommendation and about operational impacts if multi‑dose vials were discouraged [9] [10]. HHS framed the removal as restoring public trust and eliminating mercury from flu vaccines [3].
7. Practical implications for clinicians and patients
For most people in the U.S. in 2025, single‑dose, preservative‑free flu vaccine options were available and recommended; multi‑dose vials that historically have contained thimerosal were a small portion of supply and were explicitly not recommended by ACIP for broad use that season [1] [2]. If you need a definitive preservative status for a specific lot or product, the cited CDC and FDA pages indicate that checking product labeling or manufacturer statements is appropriate because public summaries do not list every marketed presentation [4] [5].
Limitations: these sources give programmatic guidance, supply projections and historical context but do not list each 2025 product and lot‑level preservative status; available sources do not mention a complete product‑by‑product table in the provided pages [1] [5].