Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services immediately for signs of a severe allergic reaction, such as:
Difficulty breathing or wheezing
Swelling of the face, lips, tongue, or throat
Widespread hives with breathing problems, dizziness, or vomiting
Collapse, severe weakness, or loss of consciousness
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Seek urgent medical advice if you develop a high or persistent fever, worsening swelling, unusual weakness, or another symptom identified in the vaccine-specific information you received.
3
Does any of this apply?
Book an appointment
Contact your healthcare team during routine hours if these reactions are not improving, last longer than expected, or concern you.
The article also says
Mild soreness, tiredness, headache, or a low fever can usually be managed with rest and observation.
Report any serious or unexpected reaction to your healthcare team.
They can assess it and explain the local vaccine safety reporting process.
Every sign above is quoted from the sofidex article on Vaccines - immunizations. If you are not sure, err upward — it is always reasonable to be checked.