What should you know about flu shot fever?

Vaccination trains the immune system to recognise influenza without giving you influenza. During that process, some people develop a mild temperature, chills, tiredness, headache, or muscle aches. A fever that starts later may instead come from an infection that happened around the same time, because protection from vaccination is not immediate.

Use a thermometer if you feel hot or shivery, drink fluids, rest, and wear light clothing. Do not give aspirin to a child or teenager unless a clinician specifically advises it. A pharmacist can help you choose an age-appropriate medicine and dose; follow the label and mention pregnancy, allergies, and long-term conditions. Avoid driving if fever or dizziness affects concentration.

Arrange medical advice if the fever is high, keeps rising, lasts longer than expected, or comes with worsening cough, severe headache, repeated vomiting, or dehydration. Seek urgent help for breathing difficulty, facial or throat swelling, collapse, seizure, confusion, blue lips, or a child who is unusually difficult to wake. These signs require assessment rather than home monitoring.

Ask what temperature or duration should prompt a review for your age group, which medicines fit your medical history, and whether your symptoms could represent an infection unrelated to the vaccination. Ask how to monitor a child or dependent adult safely.