(That's -112 F, for anyone else wondering.)
They do stability studies on these molecules, holding samples at different temperatures and measuring how much "is left" after a period of time.
This particular RNA sequence and carrier might be particularly unstable, so it require -80C if you want it to last longer than a few weeks.
In a biological context, the vast majority of RNA use falls within the 'central dogma' of DNA -> RNA -> Protein. It is merely an intermediate, albeit one with important and complex regulatory processes.
In RNA viruses and other contexts where stability is required, the RNA is stabilized by its environment, namely by associating with special proteins.
If that temperature could be obtained with dry ice, that would simplify things a bit. But AFAICT dry ice sublimates at -78.5C.
But what kind of capacity can they handle? I imagine the scale of a Covid vaccine rollout would overhelm prior existing infrastructure
Of course larger institutions already have everything in place and will get shipments with less warning (but they will also get smaller shipments since they don't have to get everyone done at once)
There are numerous companies which specialize in -80C transport and shipping. These containers can be used as temporary (3-7 day) storage at destinations where they do not have infrastructure.
So this vaccine can be distributed to regions with the infrastructure to store it and we can preserve vaccines with less stringent requirement for developing countries, etc.