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What to do if…
you suspect you have a serious reaction after a vaccine or injection

Produced and maintained by PanicStation.org Published: Last reviewed: Editorial policy UK guide

Short answer

If you may be having a severe allergic reaction, or you feel seriously unwell, call 999 now. If it is not immediately life-threatening but you are worried, use NHS 111 where available, or your local urgent-care route in Northern Ireland, for same-day advice.

Do not do these things

  • Don’t wait it out if symptoms are severe, sudden, or getting worse.
  • Don’t drive yourself to urgent care or A&E if you feel faint, short of breath, confused, have chest pain, or feel unsafe to drive.
  • Don’t take more than the label dose of painkillers, antihistamines, or other medicines.
  • Don’t take another dose, booster, or related injection until you have had medical advice about this reaction.
  • Don’t rely on social media posts to decide whether you need urgent care.

What to do now

  1. Check for emergency warning signs.
    Call 999 if you have sudden swelling of the lips, mouth, face, tongue or throat; fast or difficult breathing; wheezing; tightness in the throat; difficulty swallowing; collapse or fainting; sudden confusion, drowsiness or severe dizziness; severe chest pain; or you feel you may pass out. Tell the call handler you recently had a vaccine or injection and are worried about a serious reaction.

  2. Use an adrenaline auto-injector if you have one for this kind of reaction.
    If you have a prescribed adrenaline auto-injector, use it as instructed and call 999. Lie down if you can; if breathing is difficult, sit with your shoulders raised, and do not stand or walk around while waiting for help.

  3. If it is not an emergency, get same-day clinical advice.
    Use NHS 111 online or call 111 where this is available. In Northern Ireland, use your local urgent-care route, such as GP out-of-hours or Phone First, unless it is an emergency. Say:

    • what vaccine or injection you received, if you know;
    • when you received it;
    • what symptoms you have;
    • when the symptoms started;
    • whether the symptoms are getting worse.

  4. Switch to emergency help if symptoms escalate.
    If breathing, swelling, severe dizziness, chest pain, weakness, confusion, or faintness starts or gets worse while you are waiting, stop waiting and call 999.

  5. Gather the key details without delaying care.
    Put these in a phone note or on paper:

    • vaccine or injection name, if known;
    • where it was given and which arm or body area;
    • date and time it was given;
    • when symptoms began and how they changed;
    • any medicines taken that day;
    • allergies or previous reactions;
    • batch or lot number, if it is on your record or paperwork.

  6. Take quick photos of visible symptoms.
    If you have a rash, hives, redness, or swelling, take clear photos. This may help a clinician if the symptoms fade before you are seen.

  7. Report the suspected side effect after you have sought medical help.
    When you are safe and have urgent advice or care underway, report the suspected side effect through the MHRA Yellow Card scheme online or by app. Reporting is useful even if you are not sure the vaccine or injection caused it, but it is not a way to get medical advice.

  8. Tell the place that gave the vaccine or injection.
    Let the clinic, pharmacy, GP surgery, or vaccination site know you had a suspected serious reaction and have sought medical advice. They may be able to help confirm the product name, dose, date, and batch or lot number.

What can wait

  • Deciding whether the vaccine or injection definitely caused the symptoms.
  • Researching rare side effects online.
  • Making decisions about future vaccines, boosters, or injections.
  • Writing a full timeline beyond the basic details clinicians need now.
  • Complaints, compensation questions, or formal reports beyond the Yellow Card report.

Important reassurance

It is reasonable to take sudden or intense symptoms after a vaccine or injection seriously. Getting urgent advice quickly is a precaution, not an overreaction.

Scope note

These are first steps only, to help you get to the right level of care and avoid unsafe delays. Later decisions about future doses, allergy review, specialist assessment, or formal complaints may need help from a qualified professional.

Important note

This guide is general information, not legal, medical, financial, therapeutic, or other professional advice. It is not a diagnosis. If you feel seriously unwell, symptoms are worsening, or you are unsure what is safe, use 999 or urgent medical services rather than trying to judge it alone.

Additional Resources

Closely connected guides that may be useful during the same situation or its immediate aftermath.

About this guide

This guide was produced and is maintained by PanicStation.org using its published editorial process. Official and specialist sources are checked where relevant, and AI-assisted tools may be used for drafting, organisation, and consistency checks. The site operator remains responsible for publication, revision, and removal decisions.

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