Clinical practice guidelines define adverse events as either injection site reactions or systemic events.
Most people tolerate vaccinations without significant side effects.
However, adverse events may occur. Serious events, such as those requiring hospitalization, are rare. They happen about once per 50,000 doses. Severe allergic reactions can occur after any vaccination, less than once per 100,000 doses. Systemic events are events that occur beyond the injection site, like fatigue, headache, slight fever, chills, muscle or joint pain.