Flu shot effects: what to know

After an injection, the arm may feel sore, warm, or tender, and some people feel tired, achy, or mildly feverish. These effects reflect the body's response to the vaccine and generally settle without special treatment. An inactivated vaccine does not cause influenza infection, although a person may still catch flu around the time of vaccination before protection develops.

Not every new symptom is caused by the vaccine. Timing, other infections, medicines, and existing conditions can matter. A clinician can help distinguish a short-lived local reaction from an illness that needs treatment.

Rest if you feel tired, drink fluids, and move the vaccinated arm gently. A cool cloth may ease local discomfort. If you are considering a pain or fever medicine, check that it is suitable for your age, pregnancy status, allergies, and other medicines, or ask a pharmacist.

Keep your vaccination details and note when symptoms began. Avoid scratching an irritated injection site. If the reaction is not improving, interferes with normal activity, or concerns you, contact a healthcare professional for tailored advice.

Call emergency services for difficulty breathing, swelling of the lips, face, or throat, widespread hives with faintness, collapse, or sudden severe dizziness. Seek prompt medical advice for a high fever, worsening weakness, or a reaction that is rapidly spreading. Tell the clinician when the vaccine was given and what product was used if known.

Ask which effects are expected for your vaccine, how to manage arm soreness or fever, and which symptoms require urgent help. If you had a reaction before, ask whether the product or observation plan should change.