Fever after a vaccine: what to know

Vaccines train the immune system, and some people feel warm, tired or achy afterwards. The timing and pattern vary by vaccine and person. Fever can also be coincidental, caused by an infection that began around the same time, so not every temperature rise is a vaccine reaction.

The exact product, date, dose, age and medical history help a clinician judge whether symptoms fit an expected response. Keep the vaccination record available, including the batch or brand if listed.

Encourage fluids, rest and light clothing. Measure temperature with a suitable thermometer and observe comfort, alertness, breathing and urination. Use only fever medicine recommended for the person’s age, weight and health needs; follow the label or clinician’s instructions and do not double-dose products with the same ingredient.

Seek emergency help for breathing difficulty, facial or throat swelling, collapse, a seizure, severe weakness or widespread blistering. Contact a clinician promptly if fever is severe, continues beyond the expected period given for that vaccine, the person is difficult to wake, cannot drink, or develops a concerning rash or repeated vomiting.

Ask which vaccine was given, what reactions are expected, which medicine and dose are suitable, and whether a future dose needs a special plan.