non toxic proteins of the C-19 virus are generated in the test tube, when introduced into the body, T cells are triggered into action, this process is stored biologically, thus creating an attack response if exposed to the real virus which also contains the "decoy" protein.
unfortunately, the enzymes of said protein are fragile, and must be kept very cold in order to prevent damage.
it is a long and painstaking process to figure out what the exact safe temp is for storage, thus Phizer is playing it safe by keeping the vaccine very cold. Moderna has obviously done more experiments on what the safe temp for storage is, or, they have developed a biological "coating"' for the enzyme that makes it less fragile, and thus, able to be stored at a higher temp. All this knowledge is top secret of course, as their is billions of dollars to be made, so it is hard to know what exactly is going on inside those vaccines without an electron microscope. This is one reason that law enforcement has been hired to escort the vaccine safely. Note that vaccine was produced and distributed to Africa during one of their many pandemics, this vaccine had the same low temp requirements and distribution was done without a hitch.