Sure! Remember during the COVID vaccine roll-out, the vaccines had to be kept frozen, and could only sit for 15-30min when removed from the freezer? It's been updated a bit based on field experience and trials, but you can find more info here.

Essentially, mRNA is fragile at room temp. It needs to be kept frozen or cold for long periods of storage. Developing areas won't necessarily have the equipment to keep the vaccines cold.

It's why the oral poliovaccine, which is stable at room temperature (though runs the risk of reverting to a virulent form of the poliovirus) is used so commonly in sub-Saharan Africa and India, whereas the rest of the world uses an inactivated poliovaccine that isn't as stable at room temperature.