What vaccines worldwide still use thimerosal in multi‑dose vials as of 2026?
Executive summary
Thimerosal (thiomersal) remains used primarily as a preservative in multi‑dose vials of influenza (flu) vaccines worldwide, while routine childhood vaccines in high‑income countries have been reformulated to be thimerosal‑free or contain only trace amounts [1] [2] [3]. Multi‑dose vials with thimerosal continue to be important for immunization programs in many low‑ and middle‑income countries because they are cheaper and easier to distribute, though international and national policies have been steadily restricting its use [4] [5] [6].
1. Which vaccines still contain thimerosal in multi‑dose vials: mainly seasonal and pandemic influenza
The clearest, most consistent finding across public health sources is that thimerosal is still used as a preservative in multi‑dose vials of influenza vaccines to prevent bacterial or fungal contamination when doses are drawn from an opened vial [1] [7]. In recent U.S. seasons only a small fraction of flu products were packaged as multi‑dose vials containing thimerosal, with single‑dose, thimerosal‑free formulations making up the large majority of supply (roughly 94–96% in CDC summaries) and just a few multi‑dose flu formulations carrying about 25 µg thimerosal per dose [8] [9]. Regulatory guidance still recognizes the antimicrobial utility of thimerosal in multi‑dose influenza vials [6].
2. Other vaccines: uncommon in routine schedules but present in some products and contexts
Routine childhood vaccines in the United States and many high‑income countries have had thimerosal removed or reduced to trace levels since the late 1990s and early 2000s, and several vaccines such as MMR, varicella and many inactivated polio and pneumococcal conjugates never contained thimerosal in their licensed forms [7] [10] [3]. However, the literature and advocacy groups note a third category of products: vaccines that contain trace thimerosal left from manufacturing and vaccines that are intentionally preserved with thimerosal (10–50 µg per dose) when produced in multi‑dose format for programmatic reasons—so other antigens beyond influenza can and do appear in multi‑dose formats in some markets [4] [11].
3. Global distribution: why multi‑dose, thimerosal‑containing vials persist outside high‑income markets
Global immunization programs often rely on multi‑dose vials because they reduce cold‑chain space and distribution costs compared with single‑dose prefilled syringes, and multidose packaging has been central to mass vaccination campaigns in low‑ and middle‑income countries; for that reason thimerosal‑preserved multi‑dose vials remain in the supply portfolios of organizations like Gavi and WHO, even as high‑income markets shift to single‑dose formats [4] [5] [6]. Public health agencies emphasize that preservatives are needed to prevent contamination when vials are accessed multiple times and that a large body of studies supports the safety of thimerosal at the doses used in vaccines [1] [6].
4. Policy shifts and political pressure: recent moves to limit thimerosal use in the U.S. and scrutiny abroad
U.S. policy has moved toward eliminating thimerosal from influenza vaccines distributed domestically, with HHS and ACIP actions in 2025 prompting manufacturers and providers to transition away from multi‑dose thimerosal‑containing flu vials for U.S. use; contemporaneous reporting indicates multi‑dose vials accounted for only a small share of U.S. flu shots and are being phased out for domestic distribution [12] [9] [8]. Internationally, the U.S. has at times conditioned funding or urged global partners to reduce reliance on mercury‑based preservatives, a push that intersects with advocacy campaigns that both emphasize mercury elimination and sometimes conflate safety debates with political agendas [5].
5. Conclusion and limits of available reporting
The best available, cited public‑health documentation in this set indicates that as of 2026 thimerosal remains in active use primarily in multi‑dose influenza vaccine vials and in some multi‑dose products distributed for programmatic reasons in lower‑resource settings, while routine childhood vaccines in wealthier countries are largely thimerosal‑free [1] [9] [3] [4]. Sources do not provide an exhaustive, line‑by‑line global catalogue of every vaccine brand or country practice as of 2026, so definitive claims beyond the documented prominence of flu multi‑dose vials and the programmatic persistence of multi‑dose formats globally would require targeted manufacturer and national immunization supply data not contained in the cited material [6] [4].