Q: My 2-month-old baby has a low baseline temperature. Is 37.7°C after vaccination considered a high fever?
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 baby is 64 days old. When they recently had a mild cold without a fever, their temperature was around 36.1–36.4°C, so they seem to have a low baseline body temperature. Today, they received their 2-month vaccinations, and their temperature has gone up to 37.7°C tonight. For most babies, this is considered a mild fever, but since my baby's normal temperature is lower, should I consider this a high fever and give them fever-reducing medication?
Answer:
It is completely understandable to be worried about your 64-day-old baby developing a fever after their vaccinations.
Even if your baby has a lower baseline temperature, the standard medical threshold for a fever remains the same. A temperature of 37.7°C is considered a low-grade fever. If your baby is resting comfortably, you can simply observe them without giving fever-reducing medication.
What you can do right now:
• Dress your baby in a single layer of light clothing and maintain a comfortable room temperature between 22–24°C.
• Offer breastmilk or formula frequently in small amounts to keep them well-hydrated.
• If the injection site is red or swollen, you can gently apply a cool (not ice-cold) damp washcloth to the area for about 10 minutes.
• If your baby is excessively fussy or seems uncomfortable, you may administer acetaminophen at a dose of 10–15 mg per kg of body weight. (Be sure to check the concentration on the medicine bottle label to calculate the correct dose).
Warning signs (Go to the ER or see a pediatrician immediately if you notice any of the following):
• The temperature reaches 38.0°C or higher, or the fever lasts for more than 24 hours.
• The baby is lethargic, fails to make eye contact, or is unusually difficult to wake up.
• The baby refuses to feed and has not had a wet diaper in over 6 hours.
• The baby is breathing rapidly or has bluish lips.
• The baby has an unusual, high-pitched cry or a bulging soft spot (fontanelle) on the top of their head.
A mild fever and fussiness within 24 to 48 hours after vaccination are very common reactions. However, for infants under 3 months of age, the possibility of a serious infection must always be ruled out. Please continue to monitor the observation points mentioned above. If the temperature exceeds 38.0°C or if your baby's overall condition worsens, seek an in-person medical evaluation immediately.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
