Fact Check-Pfizer is not including tromethamine in its COVID-19 vaccine to counter side-effects

Suggestions online that Pfizer’s new COVID-19 vaccine ingredient has been added to counter vaccine-related heart attacks in children are unfounded. Pfizer, along with independent health experts, told Reuters the ingredient is a common buffer agent used to extend a drug’s shelf life.

Social media users have suggested the pharmaceutical giant “quietly snuck” the chemical compound tromethamine into its COVID-19 vaccine for children, as it is “used to stabilize people with heart attacks” (here).

One user added: “So their death jab causes heart attacks and blood clots… but instead of recalling it, they just sell more medication$!?”

The same suggestion has been repeated on Facebook and Twitter here , here , here and here , with one person saying Pfizer’s decision was “evil” (here).

While it is true to say tromethamine can be used to treat metabolic acidosis, a condition linked in some cases to heart bypass surgery (, it is also a common stabilising ingredient, known as a tris buffer, in vaccines, medications and other non-medical products (here).

One of the biggest disadvantages of the Pfizer/BioNTech mRNA vaccine for COVID-19 is its strict storage requirement at ultra-low temperatures. Once thawed, the formulation is left with a month-long shelf life in a refrigerator (here and here).

The company told Reuters in an email that replacing the vaccine’s phosphate-buffered saline for a tris buffer would elongate this time period.

“Simply put, this allows the mRNA to resist being degraded for a longer period of time before administration - meaning the pediatric vaccine can be stored for 2-8°C in commonly available refrigerators for up to 10 weeks,” a Pfizer spokeswoman said.

“This buffer will also be used in the updated adult/adolescent 30mcg doses in due course, helping to ensure simplified handling of the vaccine across age groups.”

She added: “The manufacturing processes involved in producing the pediatric doses remain unchanged from the adult and adolescent doses. There are also no changes in raw materials, mRNA, lipids or suppliers in the manufacturing of the drug substance and lipid nanoparticles (LNPs).”

Experts at Meedan’s Health Desk, a group of public health scientists working to tackle medical misinformation online, pointed out that tromethamine is also used as a stabiliser in Moderna’s COVID-19 shot, as well as other vaccines and medications.

These include the vaccines for Ebola, dengue and smallpox, and the diabetes medication known as Humalog.

“Beyond the medical industry, tromethamine is also used as a stabilizer in fragrances and cosmetics,” the Meedan scientists told Reuters via email. “Previously, the Pfizer COVID-19 vaccine for older age groups used another buffer called phosphate-buffered saline (PBS). The addition of tromethamine is meant to help prolong storage times and is considered a minor change to the vaccine formula.

“In summary, the updated formulation of the Pfizer COVID-19 vaccine with tromethamine is safe and has received FDA-approval. Health experts continue to recommend COVID-19 vaccination for the vast majority of people because the benefits of protection far outweigh the potential risks of side effects.”


Partly false. Tromethamine is a common buffer agent added to vaccines and medication. Its addition to the Pfizer/BioNTech shot for COVID-19 will greatly increase the vaccine’s shelf-life.

This article was produced by the Reuters Fact Check team. Read more about our fact-checking work here.