In every injectable drug, there is an inactive ingredient called pH buffer. The purpose is to keep pH stable. The science behind this is called formulation. In Pfeizer's adult COVID vaccine, the chemical used for this purpose is phosphate-based. In their kiddie version, it's switched to a chemical named tromethamine aka Tris. (The reason behind the switch is very likely due to the smaller dosage. This would be my educated guess. To make sure, one has to ask pfeizer or FDA). Tris is not known as therapeutically active, except it can be used for acidosis when used in large quantity. Given the small injection volume ( less than half of a ml), it is unlikely Tris can be used for any meaningful therapeutic purpose. It is just for what it is always for as a pH buffer. There is absolutely no truth behind the rumor that Pfeizer uses tris to reduce inflammation.