Tromethamine in the Pfizer-BioNTech Covid-19 vaccine is not to counter side-effects but to improve vaccine stability and ease of storage


CLAIM The Pfizer-BioNTech COVID-19 vaccine for children contains tromethamine, “a heart attack medication” with “a lot of potentially serious side effects” VERDICT

SOURCE: Social media users, Facebook, Instagram, TikTok, 29 Oct. 2021  

Factually inaccurate: Tromethamine isn’t a medication to treat heart attack. Rather, it is used to regulate acidity in body fluids in cases of metabolic acidosis, which can be the result of various conditions, including bypass cardiac surgery and cardiac arrest.
Lack of context: Tromethamine has been safely used in many products, including the Moderna COVID-19 vaccine.


In October 2021, the U.S. Food and Drug Administration authorized the emergency use of the Pfizer-BioNTech COVID-19 vaccine for children aged 5 to 11. The vaccine is adapted for children and contains one-third of the dosage approved for adults. Furthermore, the vaccine for children comes in a slightly different solution that contains tromethamine. This new formulation improves vaccine stability and ease of storage, as the vaccine can be kept in the fridge for longer periods of time compared to the original vaccine.

Tromethamine is a solution that regulates pH, not a medication to treat heart attack

Pfizer-BioNTech did change the vaccine formulation for children, as detailed on page 14 of the briefing document. The new formulation is adapted for children and contains a lower dose of mRNA than the original vaccine for adults. In addition, it replaces the saline solution with tromethamine.

Tromethamine—also called Tris—is a buffer, which is a liquid chemical mixture that regulates the acidity or alkalinity (pH) of solutions. Because it regulates pH, tromethamine can prevent and treat a condition called metabolic acidosis, which turns the body fluids too acidic. Metabolic acidosis can have many causes, including cardiac arrest, cardiac bypass surgery, and pediatric cancer. Contrary to what social media posts claimed, tromethamine doesn’t treat these conditions. Instead, it reduces acidity to prevent organ damage while the patient receives the actual treatment for the condition that caused the acidosis in the first place. Thus, the claim that it’s a “blood acid producer” is false because tromethamine’s function is actually the opposite: to make body fluids less acidic.

Likewise, the role of tromethamine in the new vaccine formulation is not to prevent potential side effects of vaccination but to improve the stability of the vaccine itself by keeping its pH stable. According to the FDA briefing document, this new formulation prolongs the storage of thawed vaccine vials at a refrigerated temperature for up to ten weeks, instead of the two weeks for the original formulation. Peter Marks, director of the Center for Biologics Evaluation and Research at the FDA, explained this in a 29 October 2021 press briefing:

“We also authorized a manufacturing change for the vaccine to include a formulation that uses a different buffer, which helps maintain the vaccine’s pH, which is a measure of how acidic or alkaline a solution is, and its stability. This formulation is more stable at refrigerated temperatures for longer periods of time, and it permits greater flexibility for vaccination providers.”

The new vaccine formulation including tromethamine isn’t exclusive to children; it is also authorized and available for people aged 12 and older.

The tromethamine added to the vaccine doesn’t compromise its safety

Many posts, like this one, claimed that tromethamine has potentially serious side effects, including “respiratory depression and IV [intravenous] thrombosis”. This claim is highly misleading because it refers to patients who receive tromethamine as a treatment for metabolic acidosis. Such treatment involves intravenous infusion of about half a liter of tromethamine several times during the period of illness. But even in this case, serious side effects are rare.

In contrast, the COVID-19 vaccine for children has a total volume of 0.2 milliliters per dose, administered intramuscularly. Although the clinical trial in children didn’t use the new formulation, this change “is not considered clinically significant”, as tromethamine is present in many other products without having been associated with any safety problems. In fact, tromethamine is in the Moderna COVID-19 vaccine and several FDA-approved vaccines like the vaccines against Ebola and dengue. Furthermore, the dengue vaccine is approved for children aged nine and older. Peter Marks pointed out at the press briefing:

“The new formulation contains tromethamine, which is known as tris buffer, and it’s commonly used as a buffer in a variety of other FDA-approved vaccines and biologics, including products for use in children. The FDA-evaluated manufacturing data support the change in this inactive ingredient, and concluded it did not impact the safety or effectiveness of the product.”



Social media posts claiming that tromethamine is a heart medication with potentially serious side effects are inaccurate and misleading. Tromethamine isn’t a heart medication and its presence in the vaccine isn’t to forestall rare cases of heart inflammation reported in some COVID-19 vaccine recipients, as some claimed. Instead, this ingredient functions as a stabilizer that allows the vaccine to be stored in the fridge for a longer period of time.


This article by provides detailed information about the formulation of the Pfizer-BioNTech COVID-19 vaccine for children and the results of the clinical trial.


Published on: 12 Nov 2021 | Editor: Iria Carballo-Carbajal


November 13, 20211:00 AMUpdated 12 days ago

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

By Reuters Fact Check

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$!?”

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.


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.


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