Fever after vaccination: what is normal and when to see a doctor
A fever after vaccination is common and usually mild: it starts within a day and settles in 1 to 2 days. The exception is MMR, where the fever may only come about a week later. What matters is knowing what fits the vaccine and what does not.
Last updated: 9 October 2026
Is a fever after vaccination normal?
Yes, it is one of the most common reactions. The NHS lists swelling or pain where the injection was given, a high temperature, feeling tired or irritable, loss of appetite and sometimes diarrhoea, and says these usually get better within 1 or 2 days. The American Academy of Pediatrics (AAP) puts it plainly: redness and fever starting on day 1 or 2 after the shot is normal.
What counts as a fever and how to measure it is covered in fever in children and how to take a child's temperature. The threshold is the same: 38 °C (100.4 °F).
When the fever starts and how long it lasts
| Vaccine | When the fever comes | How long |
|---|---|---|
| most vaccines (e.g. the 6-in-1, pneumococcal, MenB) | within the first day; the AAP says usually within 12 hours | 1 to 2 days |
| MMR (measles, mumps, rubella) | around 7 to 11 days after the jab (NHS), 6 to 12 days per the AAP, sometimes with a blotchy measles-like rash | usually 2 to 3 days |
| chickenpox and MMR (AAP) | fever and rash possible 1 to 4 weeks after the shot | short |
After MMR the NHS also describes swollen glands and joint pain around 2 to 3 weeks after the jab. A late fever like this does not mean the vaccine failed.
What to do if your child has a fever after a vaccine
- Fluids: often and in small amounts; for a breastfed baby, breast milk is best (NICE).
- Clothing: light layers, no wrapping in blankets, but do not strip the child either (NICE, NHS).
- No cooling: no baths, no sponging, no fan pointed at the child (UKHSA, NICE).
- Medicine if the child is distressed: the NHS says you can give children's liquid paracetamol (acetaminophen in the US) or ibuprofen. NICE: give a fever medicine when the child appears distressed, not just to bring the number down. Take the dose from your product's leaflet table, see the dose calculator and the paracetamol dose guide. Mind the age limits in the leaflets: under 3 months, paracetamol only on a doctor's advice and no ibuprofen.
- No aspirin for children under 16 unless a doctor prescribes it (NHS).
- Write it down: the time of the jab, the vaccine name, each temperature reading with the method and any medicine given. These are the first questions a doctor or a reaction report will ask.
MenB and paracetamol
The MenB vaccine often causes a fever, especially when given with the other routine vaccines at 2 and 3 months. That is why in the UK the NHS recommends several doses of liquid paracetamol after the MenB jab for babies at 8 and 12 weeks, following the instructions of the nurse who vaccinates. It is part of the UK schedule.
Elsewhere, including Poland, whether to give paracetamol after MenB is up to the doctor or nurse who vaccinates your child. Ask before you leave the clinic and get the dose for your baby's weight. Under 3 months, paracetamol leaflets allow it only on medical advice.
When the fever is probably not from the vaccine
A vaccine does not protect against the everyday infections a child can pick up at the same time. A fever that does not fit the timing above deserves the same assessment as any other:
- it starts more than 2 days after the jab (outside the MMR and chickenpox window): the AAP says call your doctor,
- a high temperature lasts more than 48 hours after the MenB jab: the NHS advises an urgent GP appointment or NHS 111,
- the fever lasts more than 3 days or comes back after more than 24 hours without one (AAP),
- other symptoms appear: cough with fast breathing, vomiting, ear pain, a rash that does not fade under a glass.
Red flags: get help now
- A baby under 3 months with 38 °C or more. NICE notes that some vaccines cause fever at this age, yet still places these babies in the high-risk group. The NHS gives the same advice after MenB. Do not give fever medicine before the baby is seen (AAP).
- A baby aged 3 to 6 months with 39 °C or more (NHS).
- A temperature of 40 °C (104 °F) or higher (AAP).
- Crying nonstop for more than 3 hours; vomiting or severe crying after the rotavirus vaccine (AAP).
- Fever after a vaccine in a child with a weak immune system (AAP).
- A seizure: UKHSA says around 1 in 1000 children have a fit caused by fever after the first MMRV dose, usually in the second week. Fever medicines do not prevent febrile seizures (NICE).
- Trouble breathing, a swollen face, a floppy child or one who is hard to wake. A serious allergic reaction is rare and usually happens within minutes, while you are still at the clinic (NHS).
The full list by age is in when to see a doctor with a child's fever.
Reporting a suspected reaction
Tell your doctor or nurse first. You can also report a suspected side effect yourself:
- UK: the MHRA Yellow Card scheme, where anyone can report a vaccine side effect.
- US: VAERS, where anyone can report an adverse event.
- Poland: the doctor reports a suspected reaction (NOP, within 4 weeks of the jab) to the local sanitary station within 24 hours; parents can report to the medicines office (URPL) through its reporting system or to the manufacturer (GIS).
Common questions
How long does a fever last after vaccination?
After most vaccines 1 to 2 days. After MMR it shows up around 7 to 11 days after the jab and usually lasts 2 to 3 days.
Should I give paracetamol before the jab, just in case?
Not on your own. The exception is the UK advice on paracetamol after MenB in babies; elsewhere, ask the clinician who vaccinates.
Is 39 °C after a vaccine a worry?
UKHSA advises calling the doctor at any time the temperature reaches 39 to 40 °C or above. In a baby aged 3 to 6 months, 39 °C is also the NHS threshold for urgent advice.
What about the rash after MMR?
It usually starts between day 6 and day 12. The AAP advises calling your doctor if it lasts more than 4 days.
These numbers are conversions from leaflets and guidelines. Before giving a medicine, confirm them at the source:
- NHS: paracetamol for children · NHS: ibuprofen for children
- NICE NG143: fever in under 5s · AAP HealthyChildren.org
- Polish medicines register (URPL): official leaflets of the products listed here
- Your own country's medicines regulator and the leaflet in the box always take precedence.
Tired of keeping track on a scrap of paper?
Oh Fever records what you gave and when. Free for one child.
Shows the time since the last dose, the doses recorded in 24 hours and the leaflet tables and sentences word for word, with a link to the official leaflet. It does not calculate or suggest doses.
Download on the App StoreAlso shows the row of the leaflet table for your child's weight and age, counts down to the next dose the leaflet allows and warns before the daily limit is crossed.
Get it on Google PlayRead next
NHS: MenB vaccine
NHS: MMR vaccine
UKHSA: What to expect after vaccinations
American Academy of Pediatrics: Immunization reactions
NICE NG143: Fever in under 5s
MHRA Yellow Card scheme
This content is for information only and does not replace your doctor or the medicine leaflet. Oh Fever and this website are not a medical device. Doses on this page come from the dosing tables in the leaflets of products registered in Poland, converted to millilitres and rounded to the syringe marks, never above the table. Check the strength on the package before giving any medicine. For high fever, any fever in an infant under 3 months, or worrying symptoms, contact a doctor.