Flu Shot Side Effects: What to Expect

The injected vaccine cannot give you influenza. A sore arm, tenderness, mild swelling, tiredness, headache, muscle aches, or a low fever can occur as your immune system responds. These effects generally settle without treatment. Reactions vary from person to person, and some people have no noticeable symptoms.

Tenderness at the injection site reflects a local immune response and may make the arm uncomfortable when you move it. Feeling tired or achy can happen while the body builds an immune response. A mild fever after vaccination is different from influenza, which commonly causes a broader illness with symptoms such as cough, sore throat, and pronounced fever.

The flu vaccine does not protect against every respiratory virus, so a cold or another infection can still happen after vaccination. If symptoms are intense, keep worsening, or do not begin to improve, contact a clinician for advice.

Rest if you feel tired, drink fluids, and use a cool, clean compress over a sore injection site. Gentle movement of the arm may reduce stiffness. Wear comfortable clothing and avoid pressing or rubbing the area.

If you need medicine for pain or fever, ask a pharmacist or clinician which option suits you, especially if you are pregnant, have a long-term condition, or take regular medicines. Do not take antibiotics for ordinary vaccine reactions; they do not treat an immune response.

Call emergency services immediately for trouble breathing, wheezing, swelling of the lips, tongue, face, or throat, widespread hives, fainting, or sudden severe weakness after vaccination. These may signal a serious allergic reaction.

Seek prompt medical advice for a high or persistent fever, rapidly increasing redness or swelling, severe weakness, or symptoms that concern you. Tell the clinician when the vaccine was given and describe how the symptoms changed. A healthcare professional can also advise whether a future dose needs special planning if you previously had a serious reaction.

Ask: Which symptoms should I expect with this vaccine? What can I take for discomfort given my health conditions and medicines? Does a past vaccine allergy change which flu vaccine I should receive? When should I contact the clinic if my reaction continues?