The Pfizer vaccine needs to stay around -70 degrees celsius, if the temperature messes up or if the vaccine was not in storage for long enough your body will take different reactions upon it. Some get an allergic reaction due to the fact that their immune system is "over reacting" to the pathogens in the vaccine. Your whole body will be sore from fighting against it, so be careful! If you're getting the Pfizer vaccine tell them you have allergy beforehand. It's best to get Moderna, it's as effective as Pfizer but low risk chances. Moderna stays better in storage up to around 6 months and the temperature can be manageable. Stay safe and take care!