A recurring claim online states:
“Vaccines still contain mercury-based preservatives.”
This claim usually refers to thimerosal, a mercury-containing compound historically used as a preservative in multi-dose vaccine vials to prevent bacterial and fungal contamination.
In 1999, U.S. public health agencies recommended removing or reducing thimerosal from vaccines as a precautionary measure, prompted more by an effort to reduce total mercury exposure in infants across all sources than by evidence of harm at the doses used. By 2001, thimerosal had been removed from, or reduced to trace amounts in, all vaccines routinely recommended for children under six, with one notable exception.
Some multi-dose vials of influenza vaccine still use thimerosal as a preservative, since multi-dose vials carry a contamination risk across repeated punctures that single-dose vials don't. Single-dose, preservative-free flu vaccine formulations are also widely available and contain no thimerosal. A person can typically request or receive the preservative-free version, particularly for young children, though availability varies by location and provider.
Stated as a blanket claim about “vaccines” generally, this overstates the current picture. The routine childhood vaccine schedule has been thimerosal-free or trace-only for over two decades. The claim is accurate only for a narrower case: some multi-dose flu vaccine vials.
The claim is true for a specific case, some multi-dose flu vaccines, but false as a general statement about vaccines as a category. Most routinely recommended vaccines, including the full standard childhood schedule, have not contained thimerosal since the early 2000s.
Feb 17, 2026 — Published.