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What to do if…
you suspect you may have a serious side effect from a vaccine or injection

Short answer

If you have any signs of a severe allergic reaction (like trouble breathing or swelling of the face/throat) or you feel seriously unwell, call 999 now. If it’s not immediately life-threatening but you’re worried, contact NHS 111 urgently for advice on what to do next.

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/A&E if you feel faint, short of breath, confused, or unsafe to drive—get help or call 999/111.
  • Don’t take more than the label dose of painkillers, antihistamines, or other medicines “to push through,” and don’t add new medicines to “test” what helps if you’ve had reactions before.
  • Don’t take a second dose/booster or another injection until you’ve had proper medical advice about this reaction.
  • Don’t rely on social media anecdotes to decide if you need urgent care—use NHS services.

What to do now

  1. Check for emergency warning signs (act fast if any are present).
    Call 999 if you have trouble breathing, swelling of the lips/face/tongue/throat, widespread hives with breathing/voice changes, collapse/fainting, severe confusion, or you feel you might pass out. Tell the call handler you recently had a vaccine/injection and you’re concerned about a serious reaction.
    If you already have a prescribed adrenaline auto-injector (for example an EpiPen), use it as instructed and call 999.
  2. If it’s not an emergency, get same-day clinical advice.
    Call NHS 111 and describe:
    • what you received (vaccine/injection name if known),
    • when you received it (time and date),
    • what symptoms you have and when they started,
    • whether symptoms are worsening.
      Follow their guidance (they may advise self-care, a pharmacist/GP, an urgent treatment centre, or A&E).
  3. If symptoms are escalating, switch to urgent.
    If you’re getting worse while waiting (breathing, swelling, severe dizziness, severe chest pain, new weakness, confusion), stop waiting and call 999.
  4. Gather the key details while you can (this helps clinicians quickly).
    Put in one note (phone note is fine):
    • vaccine/injection name and dose (if you know it),
    • where it was given (site/clinic/pharmacy) and which arm/area,
    • the time symptoms began and how they changed,
    • any other medicines taken that day,
    • any history of allergies or prior reactions.
      If you have it, also record the batch/lot number from your vaccination record or paperwork.
  5. Document visible symptoms (quickly, calmly).
    If you have a rash/swelling, take clear photos. This can help clinicians even if it fades later.
  6. Report it (after you’ve sought care).
    Once you’re safe and have medical advice, report the suspected side effect to the MHRA Yellow Card scheme (online or via the app). Reporting is useful even if you’re not sure the vaccine/injection caused it.
  7. Tell the place that gave the vaccine/injection (briefly).
    Let them know you had a suspected serious reaction and have sought advice/care. They may want the details for their records and may be able to help confirm the batch/lot number.

What can wait

  • Deciding whether the vaccine/injection “definitely caused” the symptoms.
  • Writing a long timeline or gathering lots of background—start with the basics only.
  • Debating next vaccines/boosters; that decision belongs after you’ve been assessed.
  • Complaints, compensation questions, or online research—focus on your health first.

Important reassurance

It’s understandable to feel alarmed—new or intense symptoms after a jab can be frightening. Getting urgent advice quickly is a sensible, precautionary step, and it doesn’t mean you’re overreacting.

Scope note

These are first steps to keep you safe and get you to the right level of care. Follow-up decisions (future doses, allergy assessment, specialist review) can be made once you’ve been medically assessed.

Important note

This guide is general information, not a diagnosis. If you feel seriously unwell, symptoms are worsening, or you’re unsure what’s safe, use NHS urgent services (111/999) rather than trying to judge it alone.

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