Q: High fever of 39.8°C after 12-month vaccinations. Is it safe to just monitor at home if it hits 40°C?
Updated: Sep 7
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 child had their 12-month vaccinations (Meningitis and Hepatitis A) this morning. Around 5 PM, their temperature was 38.7°C, so I gave them acetaminophen at 6 PM. It stayed around 38°C, so I assumed it was dropping and let them sleep. However, I just checked their temperature again, and it is 39.8°C! I hurriedly gave them dexibuprofen just now. Should I just monitor them for now? Is it okay to just watch them at home even if the fever goes over 40°C?
Answer:
You must have been very startled by the sudden high fever after your child's vaccinations.
[What to do at home right now]
• Record the exact time you gave the dexibuprofen and check their temperature again in 30 to 60 minutes.
• Dress the child lightly in a single layer of clothing and keep the room at a comfortable temperature.
• If they are awake, offer frequent, small amounts of water, breast milk, or formula to keep them hydrated.
• Do not wipe the child down with wet towels or lukewarm water, as this is no longer recommended.
[Go to the emergency room tonight if you notice any of the following]
• Shortness of breath or chest retractions (the skin pulling in under the ribs when breathing).
• The child is difficult to wake up or appears extremely lethargic and floppy.
• No urination for more than 8 hours.
• Convulsions or seizures (shaking of the arms and legs).
• A high fever that does not improve after 24 hours.
[Understanding post-vaccination fevers]
• A fever in the 38°C range (and occasionally reaching 39°C or higher) is a common immune response within 24 to 48 hours after receiving vaccines.
• The child's overall condition—such as their hydration level, responsiveness, and breathing—is much more important than the exact number on the thermometer.
• Even if the temperature reaches 40°C, if the child is drinking fluids, waking up, and responding normally, it is not necessarily an immediate emergency. However, if any of the warning signs listed above appear, they need to be evaluated by a doctor immediately.
[Fever reducer guidelines]
• Dexibuprofen can be given every 6 to 8 hours, up to a maximum of 4 times a day.
• You can cross-dose (alternate) with acetaminophen by leaving a 2 to 3-hour interval between the two different medications. However, if keeping track becomes too confusing, it is safer to stick to one type of medication and give it at regular intervals.
For now, monitor the effects of the dexibuprofen for the next hour to see if the fever begins to come down. Continue to closely observe your child's overall condition, and please seek immediate in-person medical care at an emergency room if any of the warning signs develop.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
