Fact check: New ingredient in Pfizer COVID-19 vaccine mischaracterized in online posts

Ella Lee, USA TODAY
·6 min read

The claim: Pfizer added a new heart attack-stopping chemical to kids' vaccines

As children have begun to receive their COVID-19 vaccines, questions over an ingredient change to Pfizer's vaccine have raised concerns among some online.

"Why did they add a heart attack-stopping chemical to the new jab for kids? #tromethamine," reads a Nov. 10 Facebook post, shared alongside worried-looking and heart-breaking emojis.

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Other similar posts claim the vaccine manufacturing company Pfizer changed its COVID-19 vaccine formula for 5- to 11-year-olds to include tromethamine, nicknamed tris, claiming it is a "blood acid reducer that is used to stabilize people with heart attacks." Those posts further assert the added ingredient has significant side effects such as respiratory depression and IV thrombosis.

But the key elements of these claims aren't true.

Tris buffers help maintain a vaccine's pH, or acidity, and stability, but they aren't used to stop heart attacks. And there's nothing nefarious about the formulation switch, which was made to all Pfizer COVID-19 vaccines, not just the pediatric one.

The new formulation helps the vaccine stay stable longer at refrigerated temperatures, according to Pfizer and the Food and Drug Administration. And it isn't connected to anyserious side effects.

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USA TODAY reached out to the Facebook and Instagram users who shared the posts.

Why Pfizer changed its formula

The FDA announced at an Oct. 29 press conference that Pfizer's COVID-19 vaccine had been approved for emergency use in children ages 5-11. During the same briefing, the agency announced that it authorized a manufacturing change for the vaccine.

But the manufacturing change wasn't just about the pediatric vaccine. It was a change to all Pfizer COVID-19 vaccines to allow it to be stored longer.

The new vaccine formulation includes tromethamine – a different buffer, or a solution that helps maintain a vaccine's pH, or acidity, and stability.

Dr. Peter Marks, director of the Center for Biologics Evaluation and Research at the FDA, said during the briefing that the formulation switch makes the vaccine "more stable at refrigerated temperatures for longer periods of time," which permits "greater flexibility" for vaccine providers.

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“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," Marks said.

Tris buffers are not a heart attack drug and they aren't used to counteract any alleged COVID-19 vaccine side effects. They are used in cardiac bypass surgery to "correct metabolic acidosis which may occur during or immediately following cardiac bypass surgical procedures," according to the Hazardous Substances Data Bank. The COVID-19 vaccine has not been shown to cause heart attacks, though in rare instances heart inflammation may occur.

The FDA says on its website the agency determined the new ingredient does not present "safety or effectiveness concerns."

Both the modified formulation with tris buffers and the original formulation will be available for people age 12 and older, not just young children, said Alison Hunt, a spokesperson for the FDA.

Pfizer spokesperson Steve Danehy told USA TODAY in an email that the company's goal at the beginning of the pandemic was to "get a safe, effective vaccine to people as quickly as possible." But as the vaccine has become more available, priorities have shifted.

"Improved stability has become a higher priority for the clinicians administering the vaccine," Danehy said.

He said Pfizer made "no changes" in raw materials, mRNA, lipids or suppliers in the manufacturing of the vaccine components, and the processes involved in producing the vaccine for kids "remain unchanged" from adult and adolescent doses. He also confirmed the buffer change is intended to increase storage time.

"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 at 2-8°C in commonly available refrigerators for up to 10 weeks," Danehy said.

Cameron West, 9, receives a COVID-19 vaccination at Englewood Health in Englewood, New Jersey. Health officials hailed shots for kids ages 5 to 11 as a major breakthrough after more than 18 months of illness, hospitalizations, deaths and disrupted education.
Cameron West, 9, receives a COVID-19 vaccination at Englewood Health in Englewood, New Jersey. Health officials hailed shots for kids ages 5 to 11 as a major breakthrough after more than 18 months of illness, hospitalizations, deaths and disrupted education.

There aren't any particularly strong side effects for it, either. People who receive tris buffer injections might expect to experience dizziness, feeling anxious, increased hunger or lack of appetite, according to the Cleveland Clinic. Other side effects could include confusion, fast heartbeat, flu-like symptoms or yellowing of the eyes or skin.

Hunt told USA TODAY in an email that other drugs that use tris buffers include the dengue, smallpox and ebola vaccines, plus injected medicines Enbrel and Humalog, which she said are used for children.

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Moderna's vaccine also uses tris buffer as a stabilizer, according to experts at Meedan’s Health Desk, a team of public health scientists aiming to curb online medical misinformation.

Meedan wrote that it's not unusual to find buffers like tromethamine in pharmaceutical products, including products for children, and that the ingredient is also used as a stabilizer in fragrances and cosmetics.

Our rating: False

Based on our research, we rate FALSE the claim that Pfizer added a new heart attack-stopping chemical to kids' vaccines. Tris buffers are used as part of some heart procedures, but they aren't used to stop heart attacks. And the change isn't specific to children's vaccines: Pfizer COVID-19 vaccines for all ages will use the new ingredient to increase storage life.

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This article originally appeared on USA TODAY: Fact check: Tromethamine in Pfizer vaccine mischaracterized