Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services immediately for difficulty breathing, swelling of the face or throat, widespread hives, a rapid heartbeat with severe dizziness, collapse, or loss of consciousness.
These may be signs of a severe allergic reaction.
Seek urgent medical advice if you develop new weakness, tingling, difficulty walking, or other significant neurological symptoms after vaccination.
Contact your healthcare team during routine hours if redness, swelling, fever, or pain is worsening rather than improving, lasts longer than expected, or concerns you.
Also call if you need advice about a second childhood dose or an incomplete vaccination record.
Every sign above is quoted from the sofidex article on Influenza (flu) vaccine (inactivated or recombinant) - what you need to know. If you are not sure, err upward — it is always reasonable to be checked.