Eating behavior
Is it normal for a dog to not eat the day after vaccinations
Last updated 23 September 2026 · How we write and check this
Short answer
A mild, temporary drop in appetite for a day following vaccinations is a fairly common and generally harmless reaction, similar to feeling a bit under the weather after a vaccine in people, and it should resolve within a day or two without needing any special treatment.
Why vaccines can briefly affect appetite
Mounting an immune response to a vaccine takes some of the body's resources, and a mild, short lived dip in energy and appetite is a recognized, normal part of that process for some dogs, generally resolving on its own within 24 to 48 hours.
What a normal reaction looks like
Slightly reduced interest in food, a bit more sleepiness than usual, and mild tenderness at the injection site are all within the range of a typical, mild vaccine reaction that does not need veterinary attention beyond monitoring.
What would be a more significant reaction
Complete refusal to eat lasting more than two days, vomiting, significant swelling at the injection site, difficulty breathing, or facial swelling are different from a mild appetite dip and need prompt veterinary attention rather than being assumed to be a normal post-vaccine reaction.
Key takeaways
- A mild, temporary drop in appetite for a day after vaccination is a common, generally harmless reaction.
- Slight sleepiness and mild injection site tenderness fall within a typical mild reaction.
- Refusal to eat beyond two days, vomiting, or swelling are more significant and need prompt attention.