Dog Not Eating After Vaccination: Is This Normal?

Yes, to a point — mild lethargy and a somewhat reduced appetite for 24 to 48 hours after vaccination is a common and expected response as the immune system responds to the vaccine, similar to how people sometimes feel slightly run down after a flu shot. This is generally not a cause for concern and typically resolves on its own without any intervention.

What separates a normal post-vaccine response from an actual reaction is severity and duration. A dog who eats a bit less than usual for a day but is otherwise alert and comfortable is having a typical response. A dog who refuses food entirely for more than 48 hours, develops vomiting or diarrhea, shows facial swelling, hives, difficulty breathing, or becomes significantly lethargic or unresponsive is having something beyond the expected mild reaction and needs prompt attention.

Facial swelling and hives specifically can indicate an allergic reaction to the vaccine, which — while uncommon — can develop within minutes to hours after the injection and sometimes progresses to more serious symptoms if not addressed.

What to do: For mild appetite reduction and slight tiredness in the first day after vaccination, monitoring at home without intervention is reasonable. Complete refusal to eat beyond 48 hours, vomiting, diarrhea, facial swelling, hives, or any breathing changes warrant contacting a vet promptly — most vet offices want to know about reactions to vaccines they administered regardless of severity, both for your dog's care and their own records.

If facial swelling specifically is what you're seeing, here's a full account of how a similar allergic reaction was handled in real time.