mRNA, lipids ((4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate), 2 [(polyethylene glycol)-2000]-N,N-ditetradecylacetamide, 1,2-Distearoyl-sn-glycero-3- phosphocholine, and cholesterol), potassium chloride, monobasic potassium phosphate, sodium chloride, dibasic sodium phosphate dihydrate, and sucrose.
The lipids are to allow for the mRNA to easily enter cells, the salts (sodiums) are there to help match the contents with the body (PH level etc). mRNA is difficult to keep stable and has to be kept at very low temperatures.
There is no mercury or other preservative in the Pfizer vaccine.