Tromethamine, also known as tris buffer, is a stabilizing ingredient used to increase that amount of time that pharmaceutical products can be kept in storage. The Moderna COVID-19 vaccine uses tromethamine as a stabilizer, along with other U.S. Food and Drug Administration (FDA) approved vaccines and medications (e.g. Ebola vaccine, dengue vaccine, smallpox vaccine, and diabetes medication known as Humalog).

The Pfizer COVID-19 vaccine, which was the first COVID-19 vaccine in the U.S. to receive full FDA approval beyond Emergency Use Authorization (EUA), has been reformulated to include tromethamine. When a lower dose of the Pfizer COVID-19 vaccine was approved for use with children under 12, the FDA also approved the new formulation for all age groups.

 This use of tromethamine in approved COVID-19 vaccines is safe. There is no evidence that COVID-19 vaccines with tromethamine cause serious adverse health effects. There is also no evidence that tromethamine was added to “stabilize patients” from any negative health effects of the COVID-19 vaccines. Instead, pharmaceutical companies have repeatedly stated that tromethamine is used to stabilize the vaccine itself and lengthen the time doses can be kept in storage.
 
Buffers like tromethamine are common in pharmaceutical products, including products for children. Beyond the medical industry, tromethamine is also used as a stabilizer in fragrances and cosmetics. 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.

Misinformation about the contents of COVID-19 vaccines is widespread, often causing misunderstandings about potential health impacts and hesitance in following public health guidance for vaccination. The ingredients in approved COVID-19 vaccines have been rigorously tested and reviewed for safety. It is misleading to suggest that the inclusion of tromethamine in the Pfizer COVID-19 vaccine is related to safety concerns.