Dog Vaccine Side Effects: What’s Normal, What’s Not, and When to Call the Vet

By the KertApp Editorial Team | Fact-checked against the veterinary sources listed at the end of this article

Most dogs get through their shots with nothing worse than a sleepy evening. Still, it’s natural to worry when your dog seems off after a vet visit. This guide covers the side effects of dog vaccinations by timing and severity, so you can tell a normal immune response from a reaction that needs care.

In this guide

1. Why dogs have side effects after vaccines
2. Common (mild) dog vaccine side effects
3. Signs of a severe vaccine reaction in dogs
4. Normal vs urgent: quick comparison
5. How long do dog vaccine side effects last?
6. Puppy vaccine side effects
7. Dog vaccine reactions by vaccine type
8. Which dogs are at higher risk?
9. How vets treat vaccine reactions
10. How to reduce the risk and care for your dog at home
11. Frequently asked questions
12. Sources

Why dogs have side effects after vaccines

A vaccine works by prompting the immune system to build protection against a disease. That response is a form of inflammation, so a little tiredness or soreness is a sign the body is doing its job. Vaccines are tested for safety and effectiveness before approval, but like other medical treatments they carry some risk of side effects, as the American Veterinary Medical Association (AVMA) notes.

Serious reactions are uncommon. Two large studies of pet hospital records, both led by Dr. George Moore of Purdue University, counted adverse events diagnosed within three days of vaccination. The 2005 study of about 1.2 million dogs found 38.2 events per 10,000 dogs vaccinated (0.38%, roughly 1 in 260). The 2023 study, covering more than 4.6 million dogs, found 19.4 events per 10,000 vaccination visits (0.19%, roughly 1 in 520). The two studies counted somewhat differently, but the message is the same: well over 99% of vaccination visits had no recorded adverse event.

Common (mild) dog vaccine side effects

According to the AVMA, mild side effects usually start within hours of vaccination and go away on their own. They include:

• Lethargy or sleepiness. Your dog may seem tired and less playful.
• Mild fever. Your dog may feel warm and a little “off.”
• Reduced appetite. Eating less on the first day is common.
• Soreness or mild swelling at the injection site. Your dog may flinch when touched, limp slightly, or avoid being picked up.
• A small, firm lump under the skin at the injection site. It can linger for a while. Contact your vet if it is still there after three weeks or is getting larger.
• Mild behavior changes. A sore, tired dog may be clingier, quieter, or grumpier than usual. This passes as the soreness does.
• Sneezing, mild coughing, or a “snotty” nose. These can appear 2 to 5 days after an intranasal (nose-drop) vaccine, such as some kennel cough vaccines.

Contact your vet if these signs last more than a day or two, or if your dog seems very uncomfortable.

Signs of a severe vaccine reaction in dogs

These signs usually appear within minutes to a few hours of the shot. Do not wait to see if they pass. Don’t give your dog human medicines, including antihistamines, unless your vet tells you to. The right drug and dose depend on your dog.

Normal vs urgent: quick comparison

If you’re unsure which column your dog’s symptoms fall into, call your vet. A quick phone call is always reasonable.

How long do dog vaccine side effects last?

• First few hours: The window when allergic reactions most often appear. AVMA’s client handout suggests staying at the clinic for a short while after the shot (about 30 to 60 minutes) if you can. Ask what your clinic recommends.
• First 24 hours: Tiredness, soreness, and low appetite are most noticeable.
• 24 to 48 hours: Mild side effects typically fade.
• 2 to 5 days: Sneezing or a mild cough can show up after an intranasal vaccine.
• Up to 3 days: The large studies counted reactions diagnosed within 72 hours of the shot, so keep watching your dog during this period.
• Up to 3 weeks: A small injection-site lump may linger. Call your vet if it is still there after three weeks or is growing.

If mild signs last longer than a day or two or get worse instead of better, call your vet. If your dog is sick several days after a vaccine, don’t assume it’s the shot. It may be an unrelated illness that needs its own diagnosis. For other warning signs that can appear at any time, see our guide on 5 warning signs your dog is sick and when to call the vet.

Puppy vaccine side effects

Puppies usually get a series of vaccines starting at about 6 to 8 weeks old, with boosters every 2 to 4 weeks until they are around 16 weeks. The side effects of puppy vaccines are the same as in adult dogs: sleepiness, a mild fever, a sore spot, and less appetite. For the full puppy-to-adult schedule, see our dog vaccination schedule by age.

A few puppy-specific points:

• Each visit is its own event. An easy first shot doesn’t guarantee the second or third will be the same. Watch your puppy after every round.
• Tiny puppies need closer watching. Smaller dogs had higher reaction rates in both large studies, and very small puppies can dehydrate quickly if they stop eating or drinking.
• Receiving several vaccines in one visit can increase the chance of a reaction. In the 2005 study, each additional vaccine raised risk, especially in smaller dogs. Ask your vet whether all of today’s vaccines are needed at the same visit or whether some can be spaced out.
• Keep the first day calm. Skip intense play, new places, and other stressors.
• Tell your vet about any reaction. They may adjust the schedule or split vaccines across visits.

Dog vaccine reactions by vaccine type

According to the American Animal Hospital Association (AAHA) 2022 Canine Vaccination Guidelines (updated 2024), the core vaccines for dogs are those that protect against distemper, adenovirus, parvovirus, rabies, and leptospirosis. Non-core vaccines, such as Bordetella (kennel cough), Lyme, and canine influenza, depend on your dog’s lifestyle and local disease risk. Combination shots, often written DHPP or DA2PP, cover several diseases in one injection.

Reaction rates differ somewhat by vaccine:

• Rabies: In the 2023 study, rabies vaccine had the highest adverse event rate among individual vaccines (about 24.8 per 10,000). Rabies vaccination is legally required in many places, so talk to your vet about managing risk instead of skipping it. Some veterinary researchers suggest giving rabies vaccine at a separate visit from other vaccines in dogs that have reacted before.
• Distemper and DHPP/DA2PP combinations: Mild lethargy, fever, and a sore site are the usual effects. These ranked just behind rabies in the 2023 study.
• Leptospirosis: Concerns about this vaccine are common among owners, but the 2023 study found its crude reaction rate was not higher than for DA2PP or rabies vaccines. AAHA now includes leptospirosis among the core vaccines.
• Bordetella (kennel cough): Intranasal versions can cause sneezing, coughing, or a runny nose for a few days. In the 2005 study, the injectable version had the lowest reaction rate of the vaccines studied.
• Lyme: In the 2005 study, Lyme vaccine had the highest rate among the vaccines compared. It is usually only recommended for dogs at risk of tick exposure.

Which dogs are at higher risk?

Any dog can react, but research points to a few risk factors:

• Breed. In Dr. Moore’s analysis, breed was the strongest risk factor, which suggests genetics plays a major role. In the 2005 study, Dachshunds, Pugs, Boston Terriers, Miniature Pinschers, and Chihuahuas had the highest rates. In the 2023 study, French Bulldogs and Dachshunds had the highest rates, followed by Boston Terriers.
• Small size. Reaction rates fall as body weight rises. The highest rates were in dogs weighing 5 kg (about 11 lb) or less.
• Receiving multiple vaccines at one visit. In the 2005 study, each additional vaccine raised risk by 27% in dogs up to 10 kg (22 lb) and 12% in larger dogs. Spacing vaccines when possible can help reduce this risk.
• Age and neutering. The 2005 study found higher risk in dogs about 1 to 3 years old than in puppies of 2 to 9 months, and in neutered versus intact dogs.
• A previous reaction. The AVMA advises always telling your vet about any earlier reaction to a vaccine or medication.

Having a risk factor doesn’t mean your dog will react. It means the steps below are worth discussing with your vet.

How vets treat vaccine reactions

Mild reactions usually need only rest and observation. For allergic reactions, vets can give antihistamines, corticosteroids, IV fluids, and oxygen if needed. Prompt treatment is very effective, which is why acting quickly matters.

If your dog has had a reaction before, your vet may recommend:

• Splitting vaccines across separate visits
• Pre-treating before the next vaccination
• Keeping your dog at the clinic for longer observation afterward
• Reviewing which non-core vaccines your dog actually needs

Half doses are not a safe workaround. They can leave your dog under-protected without reliably preventing a reaction, so follow your vet’s plan.

How to reduce the risk and care for your dog at home

Before the appointment

• Share your dog’s full vaccine and reaction history with the vet.
• Mention any current illness, recent medications, or health conditions. Your vet may delay vaccination if your dog is unwell.
• Book a morning appointment, so you can watch your dog during the day while the clinic is open.
• If you share your home with more than one animal, tools built for multi-pet health profile management keep each pet’s history separate.

At the clinic

• Ask which vaccines are essential today and which could wait or be spaced out.
• Stay at the clinic for a while afterward if you can, in case of an allergic reaction.

At home

• Offer fresh water and a small, familiar meal.
• Give your dog a quiet, comfortable place to rest and skip strenuous exercise for a day.
• Check the injection site gently once or twice a day for swelling, heat, or discharge.
• Don’t give human pain relievers or antihistamines without veterinary guidance.
• Keep your vet’s number and the nearest emergency clinic handy, especially after hours.

Keep a record

Write down the vaccine name, date, injection site, and anything unusual afterward. A simple log helps your vet make better decisions at future visits, especially if you see more than one vet or travel with your dog. For households with several pets, it helps to keep one profile per animal — our guide to multi-pet health profile management tools explains what to look for.

Frequently asked questions

Can vaccines make dogs sick?
Vaccines can cause mild, short-lived symptoms such as tiredness, a low fever, and reduced appetite while the immune system responds. They do not give your dog the disease they protect against. If your dog seems very ill, or signs last more than a day or two, call your vet, as something else may be going on.

Can dogs get sick after injections?
Yes, mildly and briefly. Sleepiness, feeling warm, and a sore spot are common for a day or two. Repeated vomiting, facial swelling, hives, trouble breathing, or collapse are not normal and need urgent veterinary attention.

Do dogs get sore after shots?
Yes. Soreness or mild swelling at the injection site is a common reaction. Your dog may flinch when touched, limp slightly, or avoid being picked up. It usually fades within a day or two. A small firm lump can last longer; contact your vet if it is still there after three weeks or is getting larger.

Is vomiting after a vaccine normal?
A single mild episode can happen. Persistent vomiting or diarrhea is listed by the American Veterinary Medical Association as a sign to seek veterinary care immediately, especially with weakness, swelling, or pale gums. Call your vet right away if your dog vomits more than once.

How long does a fever last after a dog vaccine?
A mild fever usually passes within a day or two. If your dog still feels hot, seems very unwell, or is not eating or drinking after two days, contact your vet.

Why is my dog shaking after a vaccine?
Mild shivering can accompany a fever or a sore injection site. Shaking that is persistent, severe, or uncontrolled, or that comes with weakness, vomiting, or collapse, may signal a serious reaction or a seizure and needs emergency veterinary care.

How long after a vaccine can a dog have a reaction?
Allergic reactions usually appear within minutes to a few hours. Mild side effects typically start within hours. The large studies on this topic counted reactions diagnosed within three days of vaccination, so keep a close eye on your dog for 72 hours.

Can a dog have a delayed reaction to a vaccine?
Less often, signs appear later. For example, painful swelling of the lower leg bones in young dogs, within a week or two of vaccination, has been reported in some large breeds. If your dog is unwell several days after a shot, with fever, vomiting, limping, or lethargy, see your vet. It may or may not be linked to the vaccine, and either way it needs a proper diagnosis.

Are there long-term side effects of dog vaccines?
Most safety research tracks reactions in the first three days, and large studies show serious reactions are uncommon. Some immune-mediated conditions, such as IMHA and ITP, have been diagnosed in the weeks after vaccination in some dogs, but studies conflict and no strong evidence shows that vaccines cause them. Injection-site tumors are a recognized concern mainly in cats. If your dog has had an immune-mediated disease, talk to your vet about risks and benefits before the next vaccine.

What are the signs of a severe vaccine reaction in dogs?
Look for facial swelling, hives, persistent vomiting or diarrhea, difficulty breathing or severe coughing, pale gums, collapse, or seizures. These need emergency care immediately. Do not wait to see whether they improve.

Will a half dose of a vaccine prevent a reaction?
No. A smaller dose can leave your dog under-protected without reliably preventing a reaction. If your dog has reacted before, ask your vet about other options, such as spacing vaccines across visits or pre-treatment.

The bottom line

Dog vaccine side effects are usually mild and short-lived, and the vaccines protect against serious, sometimes fatal diseases. Know what’s normal, watch your dog closely for the first day, and call your vet quickly if anything looks wrong. If your dog has reacted before, tell your vet so the plan can be adjusted.

This article is for general information and does not replace advice from your veterinarian. If you think your dog is having a severe reaction, seek emergency veterinary care immediately.

Sources

• American Veterinary Medical Association, Vaccinating Your Pet: avma.org/resources-tools/pet-owners/petcare/vaccinations
• Moore GE, et al. Adverse events diagnosed within three days of vaccine administration in dogs. J Am Vet Med Assoc. 2005;227(7):1102-1108.
• Moore GE, Morrison J, Saito EK, Spofford N, Yang M. Breed, smaller weight, and multiple injections are associated with increased adverse event reports within three days following canine vaccine administration. J Am Vet Med Assoc. 2023. doi:10.2460/javma.23.03.0181
• American Animal Hospital Association, 2022 AAHA Canine Vaccination Guidelines (updated 2024): aaha.org