Fever after shots: is this still normal?

How the checker decides

It works through three questions, always in this order.

1. Is there an emergency sign? Trouble breathing, a seizure, a rash that does not fade under a glass, a baby you cannot wake properly, swollen lips, tongue or throat with trouble swallowing or talking, blue or grey skin, weak, high-pitched or non-stop crying. Any of these means 911 (999 in the UK), whatever the timing (NHS).
2. Does a see-a-doctor rule apply? Under 3 months with 100.4°F (38°C) or more is always a call now, even straight after shots (AAP), and so are 102.2°F (39°C) or more at 3 to 6 months (NHS) and a baby who is floppy, refusing feeds or vomiting over and over. Weak, high-pitched or non-stop crying is an emergency sign. Paler skin, less reaction than usual, faster breathing, eating much less, or a temperature above 104°F (40°C) at any age mean a call the same day. Those signs come from the traffic light table in the NICE fever guideline and from the AAP.
3. Does the timing fit the vaccines? The shots of the first months are not live vaccines. Their fever starts within hours, inside the first 48, and usually lasts one to two days (CDC). MMR and chickenpox are live, so their fever comes about 7 to 12 days later (CDC). A fever outside those windows probably has another cause, so the general rules apply to it: call if it lasts more than 24 hours under age 2, or more than 3 days from age 2 (AAP). After MenB the UK leaflet allows 48 hours.

When everything fits, the checker tells you roughly when the fever should be gone and at what point to call if it is not.

What to expect after each visit

MenB (UK): given with the 8 and 12 week shots, it brings more fever than anything else in the schedule. Without paracetamol more than half of babies get a temperature, peaking about 6 hours after the visit and almost always gone within 2 days. That is why the UK leaflet draws the call line at 48 hours instead of 24 (UKHSA).

While you wait it out

• Offer feeds more often. Fluids matter more than bringing the number down.
• Dress your baby lightly and keep the room comfortable. No extra blankets to "sweat it out".
• Check the temperature again in a few hours and note the time. A reading with a time next to it is worth far more to a nurse than "it was high last night".
• Fever medicine only at the dose your pediatrician or the package gives for your baby's age and weight. The UK MenB schedule has its own paracetamol plan from the nurse.

Methodology

Timing windows come from the CDC Pink Book (DTaP and measles chapters) and the UKHSA MenB leaflet. The warning signs are the ones a parent can see in the NICE NG143 traffic light table, sorted into three levels: the NHS list of emergency signs, the rest of the NICE red column plus dehydration as "see a doctor now", and the NICE amber column as "call today". Temperature and duration lines are the AAP's, with the NHS 102.2°F (39°C) line for 3 to 6 months as see-a-doctor-now. The live-vaccine window is counted a little wider than 7 to 12 days, from day 5 to day 12, so that a fever on the edge is not labelled unrelated. The call rules still apply inside it.

Last reviewed: September 2026.