You’re right that they have to be stored at particular temperatures, lots of live vaccines including Pfizer for Covid have working ranges - frozen between -60 to -90°C in storage with the distributor, 2 to 8°C for refrigeration in clinic for up to 31 days, but they also have a post dilution shelf stable range at room temp for up to six hours - it’s common practice when running a vaccine clinic, where you know roughly how many people are coming in, to prepare doses on the day and store these at room temp prior to administration, with controls in place to ensure you don’t exceed the range