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Posts mislead on Pfizer’s new COVID-19 vaccine formula

November 5, 2021 GMT

CLAIM: Pfizer added tromethamine to its formulation for the COVID-19 vaccine for kids ages 5 to 11. Tromethamine’s side effects are severe and pose risks to human health.

AP’S ASSESSMENT: Missing context. While Pfizer’s COVID-19 vaccine for children under 12 contains tromethamine, the company is also adding the ingredient to its vaccines for adults and teens. Experts say Pfizer’s clinical trials show the new vaccine formula containing tromethamine is safe. Several other FDA-approved vaccines use tromethamine.

THE FACTS: The U.S. Food and Drug Administration on October 29 approved emergency use authorization of Pfizer’s vaccine for children aged 5 to 11. The agency also approved a new formula for Pfizer’s vaccines for both children and adults that includes tromethamine, an ingredient used to increase storage times in pharmaceutical products.

Posts circulated on Instagram and Facebook this week suggesting the new vaccine formulation was only for children and that the added ingredient posed serious medical risks to the recipient.

“Pfizer changed their formulation for 5- to -11 year old kids. They added tromethamine, a blood acid reducer that is used to stabilize people with heart attacks,” one post said. A similar post said, “Can anyone explain this to me? The vaccine was already too acidic?” The posts added that tromethamine causes adverse health conditions, including respiratory failure, IV thrombosis, blood clots, skin sloughing, and low blood sugar.

But the posts are misleading. Tromethamine is being added to the formulation for all age groups, and experts say no serious adverse events were reported during clinical studies on the new formulation.

“This new formulation is also authorized for use in individuals 12 years of age and older,” FDA spokesperson Abigail Capobiano said in an email to The Associated Press.

Capobianco added that tromethamine is used in other FDA-approved vaccines and products, including the dengue, smallpox and ebola vaccines, as well as in diabetes medication Humalog.

Moderna’s COVID-19 vaccine also contains tromethamine.

Tromethamine was added to the new formula so the Pfizer vaccines could be stored for longer periods, the company and FDA said.

“To enable extended storage time an alternative buffer is being leveraged, known as a ‘tris buffer,’” said Pfizer spokesperson Jerica Pitts. “This allows the mRNA to resist being degraded for a longer period of time before administration.” Pitts added the new formula allowed the vaccine to be stored in a refrigerator for up to 10 weeks.

Dr. Peter Marks, director of the Center for Biologics Evaluation and Research at the FDA, echoed this at a press briefing last Friday.

“This formulation is more stable at refrigerated temperatures for longer periods of time, and it permits greater flexibility for vaccination providers,” Marks said. “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.”

Pharmaceutical chemists and immunologists stressed to The Associated Press that data showed the Pfizer vaccines containing tromethamine are safe.

Joseph Glajch, a consultant specializing in analytical and pharmaceutical chemistry, said that while tromethamine “may have some effects at higher doses, it is likely that in these products it is used at much lower levels and therefore should be considered safe.”

“Clinical studies were performed with this formulation and no serious adverse events were noted in more than 3,000 patients,” Glajch added.

“The Pfizer data are super good with kids,” said Dr. Holden Maecker, professor of microbiology and immunology at Stanford University. “There are essentially no side effects in their study and they enrolled 20-30% of the kids with comorbid conditions, so obesity, diabetes — they had it all covered.”


This is part of AP’s effort to address widely shared misinformation, including work with outside companies and organizations to add factual context to misleading content that is circulating online. Learn more about fact-checking at AP.