What is a common and immediate symptom of an allergic reaction post-vaccination?

Itching is a common and immediate symptom of an allergic reaction that can occur shortly after vaccination. This symptom is often associated with hypersensitivity reactions, which can manifest as localized or generalized itching of the skin. The immune response triggered during an allergic reaction can lead to the release of histamines and other chemicals, resulting in the sensation of itching.

Other options such as fatigue, fever, and nausea, while they can occur post-vaccination, are not typically immediate signs of an allergic reaction. Fatigue and fever are more generalized responses that might indicate a systemic reaction to the vaccine, while nausea may occur due to other factors unrelated to an allergic response. In contrast, itching—specifically as an immediate symptom—points more directly to an allergic mechanism. This distinction is crucial for recognizing and managing adverse reactions following immunization.