Why is it used in the pediatric COVID-19 vaccine?

Tris, or tris(hydroxymethyl)aminomethane, is a buffer used to adjust and maintain pH balance. It is commonly used in many things like medicines, makeup, lotions etc.

Tris is now being used in the pediatric Pfizer vials because it allows the vaccine to be stable at refrigerator temperatures for longer periods of time, allowing for easier transportation and storage. It was already used in the Moderna Covid-19 vaccines.

Tris is called THAM or tromethamine when it is very rarely under specific circumstances used as a medicine as an alternative to sodium bicarbonate (baking soda) to treat severe metabolic acidosis (electrolyte/pH imbalance), such as when someone is in the ICU and in severe crisis or after a cardiac bypass surgery. It is not used as a heart medication. It is never used to treat myocarditis/pericarditis (the inflammation of the heart or membrane around the heart), which is typically treated with anti-inflammatory medicines and rest.

As always in medicine, the dose makes the poison. For instance, drinking too much H2O (water) can kill you. We would never tell anyone to stop drinking water.