Q: My 1-year-old's fever is stuck at 39°C after vaccination despite medication. Should we go to the ER?
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 12-month-old baby had vaccinations yesterday at 10 AM. They had a slight fever in the evening, which spiked early this morning. The fever isn't coming down even with fever reducers (I have been alternating medications since 1 AM), and it hit 39°C. We went to a local pediatrician who noted mild sore throat symptoms and prescribed only antibiotics. The doctor said not to give fever reducers too often so the baby can fight it off naturally, and not to give them at 38°C if the baby isn't struggling.
However, this is the first time fever reducers haven't worked at all for us. Isn't 39°C too hard on the baby? The fever is still stuck at 39°C. I gave the antibiotics, and the baby is currently napping. Should we go to another clinic for tests? I'm not sure when we should go to the emergency room or a larger hospital.
Answer:
It is completely understandable to be worried when your baby has a persistent high fever after a vaccination.
【Immediate Check: When to go to the ER right now】
If you notice any of the following, go to the emergency room (ER) immediately:
Blue lips or nails, or the skin under the ribs sucking in when breathing (retractions).
Difficult to wake up or unable to make eye contact.
No urine for 8 hours or more.
Severe fussiness or a stiff neck.
If these symptoms are not present and your baby is currently sleeping, proceed with the steps below.
【Key Points】
A high fever within 24–48 hours after vaccination is common, but since your baby is around 12 months old, the possibility of an infection must also be considered.
Antibiotics are only effective if there is a definitive bacterial infection; they do not work against viral fevers.
When you feel a fever reducer "isn't working," it usually means the fever hasn't disappeared completely. However, a drop of just 1 to 1.5°C is considered a normal and effective response to the medication.
The actual number on the thermometer (39°C) is less important than your baby's overall condition—whether they can drink water, make eye contact, or play even for a short while.
【What to do at home】
Follow Fever Reducer Intervals:
Acetaminophen: Every 4–6 hours (max 5 times in 24 hours).
Ibuprofen: Every 6–8 hours (max 4 times in 24 hours).
If alternating (cross-dosing), ensure each specific medication follows its own required interval, and space the different medications 2 to 3 hours apart.
Frequent, Small Amounts of Hydration:
Offer a sip or two of breastmilk, formula, or water every 5–10 minutes when awake.
Check that diapers are wet every 4–6 hours.
Light Clothing and a Cool Room:
Remove thick blankets and maintain a room temperature of 20–22°C (68-72°F).
Do not use lukewarm towel wipes or ice packs, as these can induce shivering and actually raise the body temperature.
Record Symptoms:
Log the time and dose of fever reducers, peak temperatures, urine frequency, intake amount, and fussiness level.
【When to Revisit the Doctor or Go to the ER】
The fever lasts for 3 days (72 hours) or more.
The baby does not look comfortable at all or continues to fuss severely even after taking fever reducers.
No urine for 8 hours or more.
Dry lips, crying without tears, or extreme lethargy.
A new rash appears or the neck becomes stiff.
→ If any of these apply, visit an urgent care center or ER today.
【Regarding Antibiotics and Additional Tests】
If antibiotics were prescribed solely for a mild sore throat, it is worth clarifying with your doctor if there was specific evidence of a bacterial infection (e.g., ear infection or tonsillar pus).
For infants around 12 months, a high fever lasting more than 48 hours generally warrants consideration for urine or blood tests.
Call your pediatrician's office and mention that the fever remains at 39°C with a weak response to medication, and ask if a re-evaluation or further testing is necessary.
If you cannot reach them during the weekend/night or feel increasingly anxious about your baby's condition, it is highly recommended to visit a local urgent care clinic or ER. Be sure to bring your baby's vaccination records and the name of the antibiotics prescribed today.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
