What Is Canine Influenza?

Canine influenza, often called dog flu, is a respiratory infection caused by an influenza A virus adapted to dogs. It spreads easily between dogs and ranges from a mild cough to pneumonia. Two strains circulate in the United States, and most dogs have no natural immunity to either.

"Now, we're all familiar with influenza because people also have their own influenza caused by the influenza virus," Dr. Long said. "In fact, pretty much every species has an influenza virus."

The two strains. The first canine strain, H3N8, was identified in racing greyhounds in 2004 after jumping from horses. The second, H3N2, arrived from Asia and caused a large outbreak in the Midwest in 2015 before spreading nationally. H3N2 is now the strain behind most outbreaks, and it is the one vets worry about more because dogs shed it for longer and it has occasionally infected cats. Because these viruses are relatively new to dogs, there is little background immunity, so nearly every dog exposed will pick up the virus.

How it spreads. The virus travels in respiratory droplets when an infected dog coughs, sneezes, or barks, and it survives on surfaces such as bowls, leashes, kennel walls, and human hands and clothing for hours. Dogs begin shedding the virus a day or two before they show any signs, which is why outbreaks move so fast through daycares, boarding kennels, shelters, and shows. H3N2 can be shed for three weeks or more, so an infected dog stays contagious well after it feels better.

Not the same as kennel cough. Kennel cough is a general term for contagious cough in dogs, most often caused by the Bordetella bacterium along with several viruses. Canine influenza is a specific virus with its own vaccine. A dog vaccinated against Bordetella is not protected against influenza, and the two illnesses look nearly identical in the early days.

What are the symptoms of canine influenza?

Coughing, sneezing, nasal discharge, lethargy, and a reduced appetite are the usual early signs, often paired with a fever. Most dogs recover in two to three weeks, but some develop pneumonia and need hospitalization. The trouble is that the early picture looks like an ordinary cold.

"Canine influenza can be a serious disease, and it often starts pretty mildly," Dr. Long said. "So oftentimes dogs can get very sick by the time we're aware that they have influenza."

The mild form. Roughly eight in ten infected dogs show signs. The most common presentation is a moist or dry cough that lingers for ten to twenty-one days, a runny nose, sneezing, and a dog that seems tired and less interested in food. Because the cough persists, canine influenza is frequently mistaken for kennel cough, and a dog may keep spreading the virus while being treated for the wrong thing.

The severe form. A smaller number of dogs develop high fever, rapid or labored breathing, and pneumonia, sometimes complicated by a secondary bacterial infection. Deaths are uncommon but do occur, most often in dogs that were already sick, very young, or elderly. Short-nosed breeds such as bulldogs and pugs tend to struggle more with any respiratory illness.

Diagnosis and treatment. Your vet can confirm canine influenza with a swab sent for PCR testing, ideally within the first few days of illness. There is no specific antiviral for dogs, so treatment is supportive: rest, fluids, nutrition, and antibiotics if a bacterial infection develops on top of the virus. An infected dog should be kept away from other dogs for at least three to four weeks so it does not seed a new outbreak.

When to be seen. A dog that starts coughing within a week or two of daycare, boarding, grooming, or a dog park visit should be checked rather than watched. Book an appointment if you notice these signs, and let the clinic know your dog is coughing so they can bring you in without exposing other patients. If you are unsure whether what you are seeing warrants a visit, Modern Animal All Access and Essential members can reach our team anytime through 24/7 Virtual Care.

Does every dog need the canine influenza vaccine?

No. It is a lifestyle vaccine, which means your vet recommends it based on your dog's exposure to other dogs rather than giving it to every patient. The more dogs your dog meets, the stronger the case for vaccination.

"The vaccination against canine influenza is not given to all dogs," Dr. Long said. "It is considered a lifestyle vaccination, which means that you're going to have a conversation with your veterinarian about whether your dog should be vaccinated against influenza."

Core versus lifestyle. Core vaccines such as rabies, distemper, parvovirus, and adenovirus are given to every dog because the diseases are widespread, severe, or a risk to people; our guide to core vaccines for dogs covers those in detail. Leptospirosis has moved into the core group as well. Lifestyle vaccines, including canine influenza and Bordetella, are recommended when a dog's routine puts it in contact with the disease.

Dogs that should be vaccinated. "The decision to vaccinate against canine influenza is typically made based on your dog's lifestyle, including factors such as how much contact does your dog have with other dogs," Dr. Long explains. In practice, that means dogs that go to daycare, board at a kennel, visit the groomer, spend time at dog parks, attend training classes or dog shows, travel with you, or live in a multi-dog household where one dog does any of those things. Many boarding facilities and daycares now require the vaccine, so check their policy early.

Dogs that may not need it. A dog whose social life is limited to the family and a walk around the block has a low risk of exposure, and your vet may reasonably recommend skipping the vaccine. That can change. If you are planning a trip that involves boarding, adopting a second dog, or starting daycare, tell your vet a month or more in advance so there is time to complete the initial series before the exposure begins.

Local outbreaks. Risk also rises when influenza is actively circulating in your area. Outbreaks have occurred across the states where Modern Animal has clinics, including California, Texas, Colorado, and Arizona, and during one your vet may recommend vaccination for dogs that would not otherwise need it.

How does the canine influenza vaccine work

The vaccine contains inactivated virus from both circulating strains, so your dog's immune system learns to recognize them before a real exposure. It cannot cause influenza, and it works best when the initial series is finished a couple of weeks before your dog is around other dogs.

What it covers. Modern canine influenza vaccines are bivalent, meaning they protect against both H3N8 and H3N2. A dog vaccinated only against H3N8 is not protected from the H3N2 strain now responsible for most outbreaks, so ask your vet to confirm your dog is receiving the bivalent product.

What it does. Like the human flu shot, the canine influenza vaccine reduces the chance of infection, and in dogs that do get infected it shortens the illness, lowers the severity, and reduces how much virus the dog sheds. Vaccinated dogs are also less likely to pass the virus to others at daycare or the park. It is not a guarantee against infection, and a vaccinated dog that starts coughing still needs a visit.

How long protection lasts. Immunity builds over the two weeks after the second dose and lasts about a year, which is why the vaccine is boostered annually. Timing the series around boarding or daycare start dates is important.

What does the canine influenza vaccine schedule look like?

Two doses to start, two to four weeks apart, then one dose every year. The Modern Animal app tracks the timing so you do not have to.

"If your dog does need the canine influenza vaccination, don't worry, the Modern Animal app will help you keep track of when it's time to vaccinate, which we typically do on a yearly basis," Dr. Long said.

Puppies. Puppies can begin the series at around 8 weeks of age, often alongside their core vaccine appointments, with the second dose two to four weeks later. Because full protection is not in place until about two weeks after the second dose, puppies should hold off on daycare and dog parks until the series is complete.

Adult dogs starting for the first time. An adult dog that has never had the vaccine receives the same two-dose start. If the second dose is missed by more than a few weeks, ask your vet whether the series needs to be restarted.

Staying current. After the initial series, the annual wellness visit is the natural time to renew it. If a booster lapses by a few weeks, one dose is usually enough; if it lapses by a long stretch, your vet may recommend restarting. Facilities that require the vaccine typically want a date within the past twelve months, so schedule the booster ahead of any planned boarding.

Keeping records handy. "Don't forget that the app contains a full record of your pet's vaccination history as well as health history, and you can easily download a record of vaccinations and share with your groomer, dog parks, and dog daycares," Dr. Long said.

What should I expect after the shot?

Most dogs feel fine. Mild soreness at the injection site or a quiet day are the most common side effects, and serious reactions are rare.

Common side effects. Some dogs are a little tender where the vaccine was given, slightly tired, or less hungry for a day. A small, firm lump under the skin at the injection site can appear and usually resolves within a few weeks. These are signs the immune system is responding and do not need treatment. Because the vaccine is inactivated, it cannot give your dog the flu.

Combining with other vaccines. The canine influenza vaccine is frequently given at the same visit as Bordetella and core boosters. That is routine and safe for most dogs, but if your dog is small, elderly, or has reacted to a vaccine before, your vet may suggest spacing them out.

When to call. Facial swelling, hives, repeated vomiting, difficulty breathing, or collapse within a few hours of any vaccine are emergencies and warrant an immediate call or visit. Soreness that lasts more than a couple of days, or a dog that seems unwell beyond mild tiredness, is worth checking in about. If your dog has reacted to a vaccine in the past, tell your vet before the appointment so they can plan accordingly; Modern Animal All Access and Essential members can also raise those questions through 24/7 Virtual Care before coming in.

What does the canine influenza vaccine cost?

Vaccine costs at Modern Animal vary depending on where you live. The canine influenza vaccine is typically given as part of a wellness visit, and the overall cost of that visit depends on what else is recommended.

What affects the price. The type of visit is one factor, since a vaccine given during a wellness exam is billed alongside that exam while a vaccine-only visit is structured differently. Your dog's age and health history shape what else your vet recommends at the appointment, and any additional diagnostics are priced separately. The first-time series requires two visits; after that, it is one dose per year.

For a full breakdown of service and test pricing at Modern Animal, visit modernanimal.com/pricing. Everything is listed transparently so you know what to expect before you come in.

The bottom line. Canine influenza is a real risk for dogs that spend time around other dogs, and it has a habit of looking mild until it is not. The vaccine is not for every dog, which is why the conversation with your vet matters: they will weigh your dog's daycare, boarding, grooming, and park habits and tell you whether it belongs on the schedule. If it does, two doses get your dog protected, an annual booster keeps them that way, and the Modern Animal app keeps track of the dates and the records.

If you are not sure whether your dog needs the canine influenza vaccine, or you have boarding or daycare coming up, book an appointment and we will walk through it together. For more on vaccines and preventive care, visit the Modern Animal blog.