Recent news of Pfizer vaccine for corona needing -70C temperature, made me thinking why such a low temperature is needed for mRNA based vaccine? Are there other vaccine around which need such a low temperature?
This is the temperature at which RNA is stored for long term storage without the occurance of degradation. It is also standard lab routine to store RNA at this temperature. Conviniently, this temperature can be reached by dry ice (-78°C), which makes shipping a lot easier.
However, there are indications by Biontech themselves that the vaccine will be stable at refrigerator temperatures between 2-8°C for five days and probably even for prolonged times (see here). This is actually being tested, storing below -70°C is simply the safeguard to ensure nothing bad happens. For injection, it will have to be warmed anyways.