Fever After Vaccination in a Child: What to Expect
A mild fever after a vaccine is common and usually a sign the immune system is responding. Most appear within 24 to 48 hours and settle in a day or two. The MMR vaccine can cause a fever 5 to 12 days later. Treat for comfort, not to prevent the fever, and know the signs that need a doctor.
What is expected and normal
A mild fever after a vaccine is one of the more common reactions in young children. It usually means the immune system is doing exactly what the vaccine is designed to prompt: building a response. A low-grade fever, a bit of fussiness, reduced appetite, and extra sleepiness for a day are typical and not a cause for alarm on their own.
Most children are back to themselves within 48 hours. The fever is treated the same way as any other: for comfort, not to force the number down to normal.
Timing: when the fever appears
Timing helps you tell a normal vaccine reaction from a separate illness that happens to arrive around the same time.
Most vaccines, including the common combined infant vaccines, cause any fever in this window. It usually settles within a day or two.
The MMR (measles, mumps, rubella) vaccine is a live vaccine and can cause a mild fever, and sometimes a faint rash, about a week to ten days later. This is expected and not contagious.
A fever that starts well after the first 48 hours, for a non-MMR vaccine, is more likely to be a separate infection than a vaccine reaction. Assess it on its own merits.
Whether to give medicine
A fever reaction is expected after vaccination, though some children will not develop one at all. When it does happen, it is usually mild and settles on its own within 2 days without needing medicine. The current guidance is not to give fever medicine routinely before or straight after a vaccine just to prevent a fever, since this can slightly reduce the immune response the vaccine is meant to build.
If your child is genuinely uncomfortable, consult your paediatrician or treat the fever for comfort. For a child over 3 months, paracetamol by weight is the usual choice. Check the dose against your child's current weight rather than guessing from age.
For a baby under 3 months, do not give medicine without medical advice, and treat any fever of 38.0°C or above as needing urgent assessment regardless of recent vaccination.
→ How much paracetamol to give by weight
→ How much ibuprofen to give by weight
Keeping your child comfortable
- Offer extra fluids. Feed babies more often, and offer water or milk to older children.
- Dress them in light clothing and keep the room comfortable, not overheated.
- For a sore injection site, a cool cloth and gentle movement of the limb can help.
- Let them rest. Extra sleepiness for a day after a vaccine is normal.
- Treat the fever for comfort with paracetamol by weight if your child is over 3 months and clearly uncomfortable.
When to see a doctor
A vaccine reaction should be mild and short. Contact your doctor or polyclinic, or go to the nearest 24-hour Children's Emergency depending on how unwell your child is, if any of these apply:
A baby under 3 months has any fever of 38.0°C or above
The fever reaches 38.5°C or above, or is not settling with medicine
The fever lasts longer than 48 hours, or starts more than 2 days after a non-MMR vaccine
Your child is very drowsy, floppy, not feeding, or hard to rouse
A rash of red or purple spots that does not fade when pressed with a glass
Difficulty breathing, a seizure, or swelling of the face or mouth
The injection site becomes very swollen, hot, and spreading
Severe allergic reactions to vaccines are rare and almost always happen within minutes, while you are still at the clinic. If your child has facial swelling, breathing difficulty, or collapses at home, call 995 (Singapore's emergency number) immediately.
→ Fever in a baby under 3 months: what to do
→ Toddler fever 39°C: when to monitor vs seek help
Frequently asked questions
Is a fever after vaccination normal?+
Yes, a mild fever is a common and expected response to many childhood vaccines. It usually means the immune system is responding to the vaccine as intended. Most post-vaccine fevers are low grade, appear within 24 to 48 hours, and settle within a day or two.
How long does a fever last after a vaccine?+
For most vaccines the fever appears within a day or two and lasts up to 48 hours. The MMR vaccine is different: it can cause a fever about 5 to 12 days after the injection, because it is a live vaccine that takes longer to produce a response. A fever that starts more than 2 days after most other vaccines may be due to a separate illness.
Should I give paracetamol before the vaccination to prevent a fever?+
Giving fever medicine routinely before a vaccine to prevent fever is not recommended, because it may slightly blunt the immune response. Treat a fever if it appears and your child is uncomfortable, rather than medicating in advance. Follow any specific advice from the clinic that gave the vaccine.
When is a fever after vaccination a concern?+
Seek medical advice if the fever reaches 38.5°C or above, lasts longer than 48 hours, starts more than 2 days after most vaccines, or comes with a child who is very drowsy, not feeding, or has other warning signs. A baby under 3 months with any fever of 38.0°C or above needs urgent assessment regardless of recent vaccination.
Can I give my baby medicine for a fever after their jab?+
If your child is over 3 months and uncomfortable, you can give paracetamol by weight for comfort. Check the dose against your child's current weight. For a baby under 3 months, do not give medicine without medical advice, and treat any fever of 38.0°C or above as needing urgent assessment.
My child has a sore, red leg where the injection was. Is that the same as a fever?+
Local redness, swelling, or tenderness at the injection site is a separate, common reaction and usually settles within a few days. A cool compress and comfort help. See a doctor if the redness spreads widely, the area becomes hot and very swollen, or your child develops a high or persistent fever alongside it.