ACIP votes to remove thimerosal from flu vaccines

Thimerosal

Thimerosal, initially patented by Eli Lilly as merthiolate, has been used as a preservative in a wide range of pharmaceuticals, including vaccines, since the 1930s to prevent bacterial and fungal contamination and extend the product's shelf life.

Following the FDA Modernization Act of 1997, which mandated a review of mercury in food and drugs, the American Academy of Pediatrics and U.S. Public Health Service agencies jointly recommended that vaccine manufacturers limit or remove thimerosal from their products. This precautionary measure sought to minimize cumulative mercury exposure in infants.

Since 2001, all vaccines routinely recommended for children under 6 years are now thimerosal-free, except for multi-dose flu vaccine formulations. Tracy Beth Hoeg, M.D., Ph.D., a senior clinical science advisor at the FDA, told the committee that fewer than 5% of the flu vaccines administered last season contained thimerosal.

Because the U.S. Code of Federal Regulations requires the use of preservatives in multi-dose vials of vaccines, thimerosal is still used in all three FDA-approved multidose seasonal influenza vaccines:

• Alfluria. Contains 0.01% (24.5 mcg/0.5 mL dose, 12.25 mcg/0.25 mL dose).
• Flucelvax. Contains 0.01% (25 mcg/0.5 mL dose).
• Fluzone. Contains 0.01% (25 mcg/0.5 mL dose, 12.5 mcg/0.25 mL dose).

Jeopardizing global vaccine access

Cody Meissner, M.D., Professor of Pediatrics at the Geisel School of Medicine at Dartmouth College and the lone dissenting vote, voiced strong concerns over the committee’s recommendation.

"Thimerosal is included in most vaccines administered around the globe because single-dose vials are more expensive, and many countries cannot afford a single-dose vial."

While developed nations can afford single-dose vials, many low and middle-income countries depend on thimerosal-preserved multi-dose vials for affordable vaccination programs. These preservatives allow safe use over multiple days, reducing costs and cold chain storage requirements, which are critical factors in regions with limited healthcare infrastructure.

"I realize ACIP is focused on the United States, but the recommendations that the ACIP makes are followed among many countries around the world," he continued. "Removing thimerosal from all vaccines that are used in other countries, for example, is going to reduce access to these vaccines, and it will increase cost."

Further criticism

Vicky Pebsworth, O.P., Ph.D., R.N., volunteer director of research and patient safety at the National Vaccine Information Center, abstained from voting due to objections about the wording of the recommendation, claiming it conflated multiple issues.

"My personal view is that we should not be doing anything that restricts access to vaccines of any sort, especially those already approved by the FDA and already in the schedule," Pebsworth said.

Industry implications

The American Academy of Pediatrics (AAP), which recently withdrew from ACIP participation over concerns about committee restructuring, issued a sharp rebuke.

"This selective use of data and omission of established science undermines public trust and fuels misinformation. The science on thimerosal is settled, and the rhetoric being used to suggest otherwise is misleading and harmful," Sean O'Leary, M.D., M.P.H., head of the AAP's infectious diseases committee, said in a statement.

While thimerosal-free single-dose vaccines are standard in the U.S., multi-dose vials containing thimerosal remain essential in global vaccination campaigns due to their lower cost and logistical efficiency. Without a suitable FDA-approved replacement, experts warn that ACIP's stance could set a precedent that negatively impacts global vaccine access and public health infrastructure.

Alivia Kaylor is a scientist and the senior site editor of Pharma Life Sciences.