Hepatitis A vaccine fever: what to know

Vaccines train the immune system, and temporary warmth, tiredness, or soreness near the injection site may follow. Fever can begin after the injection and generally settles as the body completes this response. Fever is not proof that the vaccine caused an infection, and it does not mean the vaccine has given you hepatitis A.

Other illnesses can also cause fever. A cough, runny nose, rash, stomach symptoms, or exposure to someone unwell may point to another cause, such as a common cold or another infection. The timing, temperature, age, medical history, and other symptoms all help a clinician interpret it.

Rest, drink fluids regularly, and wear light clothing while you feel hot. Check your temperature with a working thermometer if you can, and note when the fever started and whether it is improving. Keep the vaccinated person comfortable rather than trying to force the temperature down.

Ask a pharmacist or clinician which fever medicine is suitable, especially for a child, pregnancy, liver disease, allergies, or other medicines. Follow the product instructions and do not give aspirin to children. Do not delay assessment if the person is becoming unusually sleepy, confused, or difficult to wake.

Seek urgent help for trouble breathing, swelling of the face or throat, widespread hives, fainting, a seizure, severe weakness, confusion, or difficulty waking after vaccination. These may indicate a serious reaction or another emergency.

Contact a clinician if the fever is high, worsening, lasts beyond the expected short recovery period, or occurs with repeated vomiting, dehydration, a stiff neck, severe headache, or a new concerning rash. Infants and people with significant immune or chronic health problems may need earlier advice.

Ask whether the fever fits the timing of the vaccination, what temperature or duration should prompt review, and which medicine and dose are appropriate for the person vaccinated. Mention prior vaccine reactions, allergies, current medicines, and any symptoms that appeared before the injection.