What type of reaction is described as a systemic reaction after vaccine administration?

A systemic reaction after vaccine administration usually refers to symptoms that affect the entire body rather than a localized response. Fever or malaise exemplifies such systemic symptoms, as they can indicate the body's immune response to the vaccine, often related to the heightened activity of the immune system as it reacts to the antigens introduced by the vaccine. This immune reaction is a normal part of developing immunity and typically manifests as flu-like symptoms.

Localized reactions, such as redness and swelling, occur at the injection site and are not systemic. Severe allergic reactions can be serious but are specific types of immune responses that may not be classified as general systemic reactions; they are typically categorized as anaphylaxis or other forms of hypersensitivity. Immediate hypersensitivity refers specifically to rapid allergic responses, which also pertains to specific immune mechanisms and does not encompass the broader systemic effects like fever or malaise.