Pfizer added ingredient used to temporarily stabilize against heart attacks to kids vaccine

From page 14 of the FDA Briefing Document (PDF warning):

the Pfizer-BioNTech COVID-19 Vaccine for use in children 5-11 years of age uses tromethamine (Tris) buffer instead of the phosphate-buffered saline (PBS)

From a description of tromethamine:

Tromethamine is a proton acceptor used for the prevention and correction of metabolic acidosis associated with various clinical conditions, such as cardiac bypass surgery\

https://treehozz.com/what-is-tromethamine-used-for

" ...Tromethamine affects the balance of water and electrolytes in the body. Tromethamine is used to treat metabolic acidosis (an electrolyte imbalance). Metabolic acidosis can have many causes. It often occurs after heart bypass surgery or cardiac arrest..."

It seems they are trying to hide some side  effects they know are coming, so they can get to more children before people say stop killing the kids please