Mild sleepiness, slightly reduced appetite, and soreness at the injection site within a day or two are common immune responses that resolve with quiet rest.
Acute allergic reactions usually appear within tens of minutes as facial swelling, hives, vomiting, diarrhea, or breathing difficulty and need immediate clinic care.
That is why staying at the clinic twenty to thirty minutes after vaccination is advised, and cats with prior reactions should be flagged in advance.
An injection-site lump lasting weeks, growing, or ulcerating needs re-evaluation; for anything uncertain, photograph it and call the vaccinating clinic.
