How long is fever normal after a vaccine, and when should I see a doctor?

Last reviewed: 2026-06-14

Quick answer

A mild fever after a jab is a common, normal reaction — it usually appears within a few hours and settles within a day or two. With the flu vaccine, for example, fever, muscle and joint aches and tiredness can begin 6 to 12 hours after the jab and last up to about two days. Manage it by resting, drinking plenty of fluids, and taking a fever reducer as directed if needed. See a doctor promptly if the fever lasts more than two to three days, runs very high, or comes with difficulty breathing, swelling of the face or throat, persistent vomiting, convulsions, or extreme drowsiness. Fever in babies and toddlers warrants more caution — check with a doctor early if unsure.

A fever after a jab usually means your body is building immunity. It's a common, normal reaction — mostly mild and short-lived.

What's normal

When it appears: usually within a few hours of the jab. With the flu vaccine, for example, fever, muscle and joint aches and tiredness can begin 6 to 12 hours after.
How long it lasts: generally settles within a day or two; flu-vaccine discomfort lasts up to about two days.

How to manage it

Rest and drink plenty of fluids.
If the fever makes you uncomfortable, take a fever reducer (such as paracetamol) as directed.
Keep an eye on the temperature and on how alert the person is.

When to see a doctor

Seek care promptly if:

the fever lasts more than two to three days, or rises instead of settling;
it runs very high (persistent high fever);
it comes with difficulty breathing, swelling of the face or throat, or a body-wide rash — signs of an allergic or severe reaction; seek care immediately;
there's persistent vomiting, convulsions, extreme drowsiness or difficulty waking.

Babies and toddlers

Fever after a jab in babies and toddlers needs more caution. The younger the child, the sooner you should check with a doctor — especially fever in an infant under three months, or fever with very poor appetite, unusual sleepiness or persistent crying.

If you're not sure whether a fever is within the normal range, the safest move is to check with your doctor or the clinic where you were vaccinated.

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