Q: Can a fever fluctuate up and down after a flu shot in a 5-year-old child?
Updated: 4 days ago
Medically reviewed by Sang Hyun Ahn, MD
Content edited by Myeongchan Kim, MD
This post is a dramatization of a question and answer session experienced by our actual medical reviewers. Please note that this content is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.
Question:
My 5-year-old received a flu shot on Wednesday afternoon. Around 24 hours after the injection, their temperature started going up and down. It hasn't been 48 hours yet since the shot was given. Can a vaccine-related fever fluctuate like this, and is it considered a normal reaction?
Answer:
Yes, it is entirely normal for a fever to fluctuate after a vaccination.
A fever occurring within 24 to 48 hours of receiving a flu shot is a common side effect. It signifies that your child's immune system is actively responding to the vaccine and building antibodies. During this process, body temperatures frequently rise and fall rather than staying at a steady level.
Typical Post-Vaccination Reactions:
Mild to moderate fever occurring within 48 hours of the shot
A fluctuating temperature pattern
Redness, warmth, or mild swelling at the injection site
Mild tiredness or general body aches
Home Care Recommendations:
Comfort Measures: If your child feels uncomfortable or fussy, you may give an over-the-counter fever reducer such as acetaminophen or ibuprofen, dosed appropriately for their weight.
Hydration: Offer plenty of fluids (water, broth, or electrolyte solutions) to keep them hydrated.
Rest: Encourage quiet play and allow them to rest as much as needed.
When to Seek Medical Care:
Contact your pediatrician or visit a clinic if you notice any of the following:
The fever persists for more than 48 hours after the injection.
The fever rises to 39.5°C (103.1°F) or higher.
Your child shows signs of breathing difficulties, extreme lethargy, or a severe headache.
The injection site develops severe swelling, spreading redness, or pus.
Since the shot was given on Wednesday afternoon, the typical window for vaccination side effects extends through Friday afternoon. As long as your child is drinking fluids, staying reasonably active, and comfortable, this fever should resolve on its own. Keep monitoring their temperature, and consult your pediatrician if the fever does not break after the 48-hour mark or if new concerning symptoms appear.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
