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. Live vaccines (MMR, MMRV, and chickenpox) 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.
Live vaccines (MMR, MMRV, and chickenpox) can cause a fever 5 to 12 days later. MMR can also cause a faint rash that is not contagious. This is expected.
A fever that starts well after the first 48 hours, for a vaccine that is not a live vaccine, is more likely to be a separate infection than a vaccine reaction. Assess it on its own merits.
A small number of children have a febrile seizure with this delayed fever. What to do if your child has a febrile seizure
Whether to give medicine
This is expected and usually settles on its own. Some children will not develop a fever at all. When it does happen, it is usually mild and gone within 2 days. Fever medicine is not given routinely before or straight after a vaccine just to prevent a fever. Follow any specific advice from your clinic or paediatrician about fever medicine after vaccines.
If your child is genuinely uncomfortable and you are unsure, consult your paediatrician. For a child over 3 months, you can give paracetamol for comfort if your child is uncomfortable or it is 38.5°C or above. 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
Use paracetamol, not ibuprofen, if dengue is possible, your child is vomiting or not drinking well, is under 3 months, or has had diclofenac. When not to use ibuprofen
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.
- If your child is over 3 months, you can give paracetamol by weight for comfort if they are uncomfortable or it is 38.5°C or above.
When to see a doctor
A vaccine reaction should be mild and short. See your GP or polyclinic the same day if any of these apply:
- The fever lasts more than 48 hours.
- The fever starts more than 2 days after a vaccine that is not a live vaccine.
- Your child seems more unwell than a mild reaction, or is feeding much less than usual.
- The injection site becomes very swollen, hot, and spreading.
Call 995 now if your child has a fever and any of these:
- !A seizure lasting more than 5 minutes (give rectal diazepam if a doctor has prescribed it, and still call)
- !Struggling to breathe (skin pulling in under the ribs, nostrils flaring, or grunting), pauses in breathing, or lips turning blue or grey
- !Cannot be woken, or floppy and not responding to you
- !A rash of small red or purple spots that does not fade when you press a glass on it
- !Swelling of the lips, tongue, or face, with any difficulty breathing
- !Cold, clammy, or mottled skin, with drowsiness or restlessness
Go to the nearest 24-hour A&E or children's emergency now if:
- !Swelling of the face, lips or tongue, even without difficulty breathing
- !A baby under 3 months with a temperature of 38.0°C or above
- !A first febrile seizure, even if it has stopped
- !After a seizure: confused, still drowsy after 30 minutes, or more than one seizure in a day
- !A stiff neck, or crying in pain when bending the head forward
- !Unusually drowsy or hard to wake, but can be woken
- !Dengue warning signs as the fever comes down: tummy pain, repeated vomiting, bleeding gums or nose, or very tired
- !No urine or wet nappy for 12 hours or more
- !No tears when crying, sunken eyes, or a very dry mouth
- !Cannot keep any fluids down
- !Green vomit
- !A temperature above 40°C that is not coming down, and your child seems unwell
Severe allergic reactions to vaccines are rare and almost always happen within minutes, while you are still at the clinic. If your child has swelling of the face or lips with any difficulty breathing, 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. Live vaccines (MMR, MMRV, and chickenpox) are different: they can cause a fever 5 to 12 days later, because they take longer to produce a response. A small number of children have a febrile seizure with this delayed fever. A fever that starts more than 2 days after a vaccine that is not a live vaccine 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 a fever is not recommended. If a fever appears and your child is over 3 months, you can give paracetamol for comfort if your child is uncomfortable or it is 38.5°C or above.
When is a fever after vaccination a concern?+
See your GP or polyclinic if the fever lasts more than 48 hours, starts more than 2 days after a vaccine that is not a live vaccine, or your child seems more unwell than a mild reaction. A baby under 3 months with a temperature of 38.0°C or above needs urgent assessment at the nearest 24-hour A&E or children's emergency, regardless of recent vaccination. Call 995 for a seizure lasting more than 5 minutes, difficulty breathing, or a rash that does not fade when pressed with a glass. You can give paracetamol for comfort if your child is uncomfortable or it is 38.5°C or above.
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 has a fever lasting more than 48 hours alongside it.