What is a common adverse reaction classified as systemic?

Fever is considered a common systemic adverse reaction because it signifies a systemic response of the body to an infection or an immune challenge, such as vaccination or medication. When the body detects pathogens or agents that it perceives as threats, it often responds by elevating the body's temperature through cytokine release, leading to fever. This systemic effect can indicate that the body's immune system is actively engaged and working to counteract the perceived challenge.

In contrast, injection site pain is typically a localized reaction associated directly with the area of administration rather than a systemic response; it affects only the local tissue and does not indicate a systemic change within the body. Swelling of the throat might suggest an allergic reaction and can have systemic implications, but it is primarily recognized as a localized symptom that can require immediate attention. Urticaria, often known as hives, is also primarily a localized skin reaction that can be part of a systemic allergic response, but it does not fit the definition of a common systemic adverse reaction in the same way that fever does. Overall, fever stands out as a clear indicator of a systemic response by the body.