Side effects that have been reported with Pfizer-BioNTech COVID-19 vaccines include: Severe allergic reactions Non-severe allergic reactions such as rash, itching, hives, or swelling of the face Myocarditis (inflammation of the heart muscle) Pericarditis (inflammation of the lining outside the heart) Injection site pain/tenderness Tiredness Headache Muscle pain Chills Joint pain Fever Injection site swelling Injection site redness Nausea Feeling unwell Swollen lymph nodes (lymphadenopathy) Decreased appetite Diarrhea Vomiting Arm pain Fainting in association with injection of the vaccine Dizziness Irritability These may not be all the possible side effects. Serious and unexpected side effects may occur. The possible side effects are still being studied.