When a dog starts vomiting and having diarrhea after a vaccine, it can feel alarming because these symptoms come on suddenly and can make your dog look miserable very quickly.
While mild stomach upset is one of the more common vaccine reactions, having both vomiting and diarrhea together means the digestive system is under real stress and needs close attention.
In this guide, we explain the most common causes of diarrhea and vomiting in dogs after a vaccine, what you can do and when to seek veterinary care.
Dog Diarrhea And Vomiting After Vaccine
Diarrhea and vomiting after a vaccine happen when the immune system’s response to the vaccine irritates the stomach and intestines.
Vaccines are designed to stimulate the immune system, and in some dogs this immune activation releases inflammatory chemicals that upset the lining of the digestive tract.
This inflammation makes it harder for the stomach and intestines to hold down food and water, leading to nausea, vomiting, loose stools, and sometimes abdominal discomfort.
Dog Diarrhea And Vomiting After Vaccine: Common Causes
Generalized Immune System Reaction
After vaccination, your dog’s immune system shifts into high gear to build protection against disease.
In some dogs, this response is stronger than expected and affects not just the immune cells but also the stomach and intestinal lining. This causes inflammation that leads to nausea, vomiting, cramping, and diarrhea.
Dogs may seem tired, unwilling to eat, and uncomfortable because their digestive system is inflamed and sensitive.
Related: Dog diarrhea after vaccines (Why it happens)
Vaccine Ingredient Sensitivity
Vaccines contain stabilizers, preservatives, and proteins that some dogs react to.
If your dog is sensitive to one of these components, their immune system may treat it as a threat, triggering inflammation throughout the body, including the gut.
This can cause vomiting, watery diarrhea, drooling, itching, or facial swelling along with digestive upset.
Delayed Allergic Reaction
Some allergic reactions to vaccines do not happen immediately. Instead, symptoms appear one to three days later as the immune system continues to respond.
During this delayed phase, inflammation can affect the stomach and intestines, causing repeated vomiting and diarrhea.
Dogs may also develop hives, red skin, fever, or low energy along with the digestive symptoms.
Stress-Related Digestive Upset
The stress of a vet visit, injections, and being handled can be enough to upset a sensitive dog’s stomach.
Stress hormones change how the intestines move and how stomach acid is released, which can lead to nausea and loose stools.
This type of reaction often shows up within a day or two of vaccination, especially in anxious or nervous dogs.
Related: Dog Vomiting After Vaccine (Here’s why)
Flare Up of an Underlying Digestive Condition
Dogs with inflammatory bowel disease, food sensitivities, or a history of vomiting and diarrhea are more likely to react strongly after vaccination.
The immune stimulation from the vaccine can worsen existing inflammation in the gut, triggering a flare-up that leads to vomiting and diarrhea.
These dogs often have mucus in their stool, reduced appetite, and belly pain.
Dehydration and Electrolyte Imbalance
Once vomiting and diarrhea start, fluid loss can quickly lead to dehydration.
As dehydration worsens, it further irritates the digestive system and can make nausea and diarrhea more severe.
Dogs may become weak, have dry gums, and seem listless if fluid loss is not corrected.
Read more: Dog Diarrhea With Blood After Vaccine (What it means)
What to Do
Allow your dog’s stomach to rest by withholding food for a short period while still offering small, frequent sips of water.
If your dog keeps water down, you can slowly reintroduce bland food such as boiled chicken and plain rice once the vomiting settles.
Keep your dog in a quiet, comfortable space to reduce stress, which can worsen digestive upset.
Watch closely for changes in energy level, hydration, and the amount of vomiting or diarrhea so you can report these details to your vet.
Never give human anti-nausea or anti-diarrhea medications unless your veterinarian tells you to, as some can be dangerous for dogs.
When to Call or Visit Your Vet
Call your vet if vomiting or diarrhea lasts more than 24 hours after vaccination.
Seek urgent care if your dog cannot keep water down, becomes very lethargic, or refuses to eat.
Go to the emergency clinic if you see blood in the vomit or stool, or if your dog shows signs of dehydration such as sunken eyes or dry gums.
Puppies, senior dogs, and small breeds should be seen sooner because they can become dangerously dehydrated very quickly.
Read more: Dog side effects after vaccines (Possible reactions explained)
Key Takeaway
Vomiting and diarrhea after a vaccine usually happen because the immune system is temporarily upsetting the stomach and intestines, but severe or ongoing symptoms can become dangerous.
Paying close attention to hydration, comfort, and symptom progression — and getting veterinary help when needed — gives your dog the best chance to recover quickly and safely after vaccination.