Seeing your dog throw up after a vaccination can be frightening, especially when they were acting perfectly normal just hours earlier.
While many post-vaccine reactions are mild, vomiting can signal that your dog’s immune system is under stress and needs careful attention.
We explain why this possible vaccine reaction may happen, what to do and when to contact your veterinarian.
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Dog Vomiting After Vaccine
Vomiting after a vaccine happens because your dog’s immune system is reacting to the injected antigens and inflammatory signals entering the body. As the immune system activates, it releases chemicals that can affect the stomach and intestines, leading to nausea and vomiting.
Some dogs experience only mild digestive upset, while others develop stronger reactions due to sensitivity, allergies, or underlying health conditions.
Stress, pain at the injection site, and immune over-stimulation can all worsen stomach irritation. In rare cases, vomiting may be the first sign of a more serious vaccine reaction that requires veterinary care.
Dog Vomiting After Vaccine: Common Causes
Immune System Inflammatory Response
Vaccines work by stimulating the immune system to recognize and fight specific diseases. This process triggers the release of inflammatory chemicals throughout the body, which can temporarily affect the digestive tract.
When these immune signals reach the stomach and intestines, they can cause nausea, cramping, and vomiting. Some dogs will vomit once and recover quickly, while others may continue to feel unsettled for several hours.
This response is more likely in dogs with sensitive stomachs or strong immune reactivity, and it explains why vomiting often occurs within 12 to 24 hours of vaccination.
Related: Dog suddenly not eating and vomiting (Here’s why)
Gastrointestinal Sensitivity
Some dogs have naturally delicate digestive systems that react strongly to changes in the body. A vaccine can disrupt the balance of gut nerves and immune cells that regulate digestion.
This can cause stomach spasms, acid buildup, and intestinal irritation that leads to vomiting even though nothing is wrong with the stomach itself.
These dogs may also drool, lick their lips, or seem uncomfortable before throwing up.
Repeated vomiting or refusal to eat afterward suggests the gut lining is more irritated than usual and should be monitored closely.
Allergic Reaction
In some dogs, vomiting is part of an allergic-type reaction to vaccine ingredients such as proteins, preservatives, or adjuvants. These reactions can range from mild to serious.
Mild allergic reactions often cause nausea, vomiting, itchiness, facial swelling, or hives. The immune system mistakenly identifies vaccine components as dangerous and releases histamine and other chemicals.
If vomiting is paired with swelling, redness, or behavioral changes, this may indicate a hypersensitivity reaction that needs veterinary evaluation.
Stress and Nervous System Response
Veterinary visits, injections, and restraint are stressful experiences for many dogs. Stress activates the nervous system, which directly affects the stomach and intestines.
This stress response can slow digestion, increase stomach acid, and trigger vomiting after the dog returns home. Some dogs vomit hours later once the adrenaline wears off and their body tries to rebalance.
Dogs that shake, hide, or appear withdrawn after vaccination may be more likely to vomit from stress alone.
Injection Site Pain and Systemic Discomfort
Vaccines often cause soreness at the injection site, along with mild fever or body aches. This discomfort can reduce appetite and trigger nausea.
When a dog feels sore, tired, and inflamed, their digestive system may temporarily shut down, leading to vomiting or regurgitation.
If your dog seems stiff, reluctant to move, or painful when touched near the injection site, vomiting may be part of a whole-body reaction to discomfort.
Underlying Health Conditions
Dogs with kidney disease, liver disease, inflammatory bowel disease, or weakened immune systems are more prone to vomiting after vaccines.
These conditions reduce the body’s ability to handle immune stress, making side effects more intense and longer-lasting. Older dogs and those with chronic illness are especially vulnerable.
In these dogs, even routine vaccines can cause significant digestive upset that should not be ignored.
Read more: Dog Trembling and Shaking After Vaccine (What it really means)
What to Do If Your Dog Is Vomiting After Vaccination
If your dog vomits once and otherwise seems alert, allow their stomach to rest for several hours before offering food. Small sips of water can help prevent dehydration, but do not force drinking.
Keep your dog calm and comfortable in a quiet area so their nervous system and immune system can settle. Avoid exercise, excitement, or stress for at least 24 hours.
When food is reintroduced, start with small portions of bland food such as boiled chicken and rice to reduce stomach irritation. Monitor for repeat vomiting or loss of appetite.
Watch your dog closely for changes in behavior, breathing, swelling, or energy level. These signs help determine whether the reaction is mild or worsening.
If your dog has a history of vaccine reactions, make a note of this for future veterinary visits.
When to Call or Visit Your Vet
Call your veterinarian if vomiting continues for more than 24 hours or occurs multiple times in a short period. Repeated vomiting can quickly lead to dehydration and weakness.
Seek immediate care if vomiting is paired with facial swelling, hives, difficulty breathing, collapse, or extreme lethargy, as these can indicate a serious allergic reaction.
Contact your vet if your dog refuses all food and water, appears painful, or shows signs of confusion or distress after vaccination.
Puppies, small dogs, and dogs with existing health problems should be evaluated sooner, even if symptoms appear mild.
Read more: Dog side effects after vaccines (Possible reactions explained)
Key Takeaway
Vomiting after a vaccine is a sign that your dog’s immune system is reacting, and in many cases it resolves on its own with rest and gentle care. However, repeated vomiting, behavioral changes, or swelling should never be ignored.
By monitoring your dog closely and knowing when to involve your veterinarian, you can protect your dog’s health while still benefiting from life-saving vaccinations.