What should I do about an allergic reaction after a vaccine?

Last reviewed: 2026-06-14

Quick answer

A severe allergic reaction (anaphylaxis) is extremely rare and usually happens shortly after the jab — which is why you're normally observed on-site for 15 to 30 minutes. If you get signs of a severe reaction such as difficulty breathing, swelling of the face or throat, a hoarse voice, a body-wide rash, dizziness or fainting, get help immediately — if you're at the clinic, alert staff at once; if you've left, call 999 or go to A&E straight away. Mild reactions (such as itchiness or a small rash at the site) usually settle on their own, but still tell your doctor for the record. Before any future jab, remember to tell your doctor you've had this reaction.

The vast majority of reactions after a jab are mild and short-lived. A true severe allergic reaction is very rare, but it's important to know the signs and what to do.

Why you're observed on-site

A severe allergic reaction (anaphylaxis) usually happens within minutes to a short time after the jab, which is why you're normally asked to stay on-site for 15 to 30 minutes afterwards. If it does happen, the staff there can treat it immediately.

Signs of a severe reaction — get help immediately

Any of the following is an emergency:

difficulty breathing, shortness of breath or wheezing;
swelling of the face, lips, tongue or throat;
a hoarse voice or trouble swallowing;
a widespread rash or hives;
dizziness, paleness or fainting.

What to do: if you're still at the vaccination site, alert the staff at once; if you've left, call 999 or go to A&E immediately. Don't drive yourself.

Mild reactions

Mild itchiness or redness at the site, or a small local rash, usually settles on its own and isn't cause for alarm — but tell your doctor so it's on record.

Future vaccinations

If you've had an allergic reaction to a vaccine, always tell your doctor the nature and severity of that reaction before any future jab, so they can assess whether it's suitable, whether to refer you, or whether to vaccinate under special arrangements.

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