What is considered a systemic reaction to a vaccine?

A systemic reaction to a vaccine is defined as a response that affects the entire body rather than a localized area. Fever is a classic example of a systemic reaction because it reflects an increase in the body's overall temperature as part of the immune response to the vaccine. When the immune system is activated by the vaccine, it can lead to systemic symptoms like fever, chills, or body aches as the body responds to the introduction of the antigen.

Tenderness at the injection site is typically a localized reaction, affecting only the area where the vaccine was administered. Wheezing and angioedema can indicate allergic reactions, but they are also not classified as systemic reactions in the context of vaccine responses. Wheezing is primarily a respiratory symptom, and angioedema is a more severe allergic response that can affect specific areas, often seen in cases of anaphylaxis. Therefore, fever stands out as the correct choice, as it indicates the body is mounting a broader immune response.