Tired after a flu shot

The immune system responds to vaccination, and some people notice tiredness, a sore arm, mild fever, headache, or muscle aches afterwards. These effects do not mean that the inactivated vaccine has caused flu. Recovery can also be affected by poor sleep, anxiety, dehydration, or an infection that was already developing before the appointment. The timing and severity of symptoms matter when deciding whether another cause needs attention.

Rest, drink fluids, and return to normal activity gradually as you feel able. Gentle arm movement may reduce stiffness around the injection site. Eat normally if you can and avoid strenuous activity while feverish or light-headed. If you need a pain or fever medicine, check the label and ask a pharmacist or clinician if you have a medical condition, take other medicines, or are pregnant. Keep a note of when symptoms began and whether they are improving.

Seek emergency help for trouble breathing, swelling of the face or throat, widespread hives, collapse, or severe dizziness soon after vaccination. Contact a clinician if fever is high or persistent, fatigue is severe, symptoms are worsening rather than easing, or you develop concerning symptoms that do not fit a mild vaccine reaction. Report any suspected serious reaction to the vaccination service or healthcare team.

Ask whether your symptoms fit the expected response, whether another illness could be responsible, and which medicines are suitable for you. Tell them about allergies, previous vaccine reactions, pregnancy, immune conditions, and every medicine or supplement you use.