Vaccine Committee Bans Mercury (Thimerosal) from Flu Vaccines!

A CDC advisory panel recommended on June 25, 2025, that the mercury-containing preservative thimerosal be removed from influenza vaccines. In theory, only about 4% of flu shots contain thimerosol. That’s because it is primarily used in multi-dose vials. In other words, if your vaccine comes in a one-and-done vial, there is nothing to worry about. But if the nurse or pharmacist uses the same vaccine vial for multiple doses, there is a good chance that this mercury-containing preservative was included to reduce the risk of bacterial contamination.

Good Riddance or Baroque Worrying?

You may not be familiar with the term baroque worrying. It was coined by a lawyer friend who meant it to signify concern about an relatively low risk. In other words, worrying that you might be hit by lightning today would be “baroque worrying” according to our friend. (Unless, of course, you are standing outside in the middle of a raging thunderstorm. Don’t do that!)

But is the preservative in some vaccines a health risk, or does it deserve the term baroque worrying? Some vaccine enthusiasts think so.

An article in STAT (June 26, 2025) describes the removal of thimerosal from flu vaccines.

It quotes a pediatrician on the new CDC Advisory Committee on Immunization Practices (ACIP). Dr. Cody Meissner teaches at Dartmouth College’s Geisel School of Medicine. He is considered a renowned expert in vaccinology.

Don’t Worry, Be Happy About Thimerosal:

The article in STAT notes that Dr. Meissner voted against the decision to only allow thimerosal-free flu vaccines on the market:

“ Meissner argued there is an abundance of scientific data showing that thimerosal, which contains ethylmercury, does not pose the risk associated with methylmercury, which one can encounter by eating diets high in fish.

“‘Of all the issues that ACIP needs to focus on, this is not a big issue,’ Meissner told his colleagues. ‘To make the industry jump through hoops for something for which there is no evidence of harm, I think, is an issue that needs further discussion.’

“Meissner also expressed concern that, in some cases, disallowing the use of multi-dose vials could mean that flu vaccine might not be available to some people.”

A Different Perspective About Thimerosal:

I happen to disagree with Dr. Meissner. So did the new ACIP committee. It voted to get the mercury-containing preservative out, despite the CDC’s long-held position that thimerosol does not cause problems such as “autism spectrum disorder or other neurodevelopmental disorders.”

But here’s the rub. The Food and Drug Administration began requiring the elimination of thimerosal from over-the-counter topical medications in the 1990s.

You have to be old, like me, to remember topical Merthiolate. Mercury had been used as an antibacterial prior to the development of thimerosal. But the Eli Lilly company especially liked the “new” mercury-containing antiseptic. It was granted a patent in 1927. Lilly marketed it under the trade name Merthiolate. The active ingredient of Merthiolate? Thimerosal.

No one seemed to worry very much about mercury toxicity (Journal of Toxicology and Environmental Health, Part B, Nov. 28, 2007):

“Thimerosal has been marketed as an antimicrobial agent in a range of products, including topical antiseptic solutions and antiseptic ointments for treating cuts, nasal sprays, eye solutions, vaginal spermicides, diaper rash treatments, and perhaps most importantly as a preservative in vaccines and other injectable biological products, including Rho(D)-immune globulin preparations, despite evidence, dating to the early 1930s, indicating Thimerosal to be potentially hazardous to humans and ineffective as an antimicrobial agent. Despite this, Thimerosal was not scrutinized as part of U.S. pharmaceutical products until the 1980s, when the U.S. Food and Drug Administration finally recognized its demonstrated ineffectiveness and toxicity in topical pharmaceutical products, and began to eliminate it from these.”

The FDA eventually determined that thimerosal posed little benefit but significant risk (In These Times, Nov. 11, 2003).

“In 1998, the FDA finally banned Thimerosal for use in OTC products—18 years after it began a safety review of mercury-containing products. It took another year before the CDC and the FDA would ask manufacturers to remove thimerosal from childhood vaccines. Eli Lilly stopped making Merthiolate-containing products in the mid-’80s but still profits from licensing agreements with pharmaceutical companies around the world.”

Merthiolate and Mercurochrome (which contained merbromin, a different mercury compound) were both staples in many medicine cabinets across America. In 1998 the FDA classified merbromin as untested and “not generally recognized as safe and effective.” Both merbromin and thimerosal disappeared from OTC topical products shortly thereafter.

The Thimerosal Paradox:

Here is the mystery. In 1998 the FDA banned mercury-containing topical products that were sold widely across the US. The reason was that an FDA safety review determined such products were not very effective and potentially toxic.

It is possible that some mercury was absorbed through the skin. There are reports of toxicity, especially when mercury-containing products were applied to wide areas or to burned or damaged skin. But topical use, as bad as it was, seems less likely to pose a serious problem than injected mercury-containing compounds.

I find it paradoxical that the FDA banned topical mercury products, but to this day does not seem to have a problem with mercury-containing influenza vaccines. Given that only 4%-6% of flu vaccines contain thimerosal, I do not understand the outcry.

According to the Washington Post, June 26, 2025:

“Scientists and public health authorities have deemed thimerosal safe, and the vast majority of flu shots don’t have it. But the removal would probably make flu vaccines more expensive and harder to receive for some Americans, public health experts said.”

Really? There is no other preservative that could be used in multi-use vials of influenza vaccine? Would it be a terrible tragedy if 4% to 6% of our flu shots disappeared? That would still leave 94% to 96% of the flu shots on the market. Single use vials might also reduce the risk for contamination.

If the FDA decided 25+ years ago that mercury-containing topical products were relatively ineffective and potentially dangerous, I do not see why the agency could not determine that mercury should not be used in vaccines. It did exactly that for children’s vaccines starting in 1999. Presumably, other vaccines rely upon non-mercury-containing preservatives. Why not use those preservatives in multi-use flu vaccines?

Final Words:

Clearly, this is a controversial topic. We would appreciate learning your take.

If you found this discussion useful, please share the article with others who may be interested. You can use the icons at the top of the page to send it by email or post it to Facebook, BlueSky or X. We’d also like to suggest that you consider subscribing to our free newsletter. You can choose whether to receive it every day, once a week or biweekly. Here’s the link: https://www.peoplespharmacy.com/subscribe