Features July 2018 Issue

Canine Influenza: Is Dog Flu Something to Worry About?

Can dogs get the flu? Should you have your dog vaccinated against the “dog flu”? The answer, it turns out, depends on your dog's lifestyle.

You just picked up your dog from boarding after a lovely vacation. Everything seems fine – and then your canine companion starts coughing. He has some nasal discharge. He feels warm, and he doesn’t want to eat. You remember that you just saw on the news that canine flu was causing problems. Oh no! You panic. Has he contracted the flu during his stay at the boarding facility?

It’s certainly possible; boarding kennels and other places where high numbers of dogs congregate are the most common place for dogs to come into contact with one of the flu viruses.

Currently, two strains of flu have been identified in dogs within the United States: H3N2 and H3N8.

The initial outbreak in 2003-2004, identified as H3N8, was restricted to Greyhounds in Florida and had a high mortality rate (38 percent). There was then a lull in cases until 2015; then, in Chicago, another outbreak occurred and was later identified as a new strain of canine flu: H3N2.

The most recent flare-up starting in mid-2017 and into spring of 2018 included both strains, though H3N2 was more prevalent and found to be more virulent. As of now, canine influenza has been reported in 40 states.

Dog Flu Symptoms

Symptoms of flu include sneezing, coughing, runny nose, fever, lethargy, and loss of appetite. About 80 percent of the dogs who are infected with the virus will have only mild symptoms, with about 20 percent of infected dogs showing no symptoms whatsoever (these dogs, however, are still able to spread the virus). Most dogs recover in two to three weeks.

In severe cases, however, the flu can progress to pneumonia. Symptoms of pneumonia are high fever; thick, purulent nasal discharge; and difficulty breathing. In severe cases, the illness can be fatal.

dog flu nasal discharge

This dog has mucopurulent discharge, likely secondary to pneumonia. Dogs who are vaccinated for the flu generally have less severe symptoms and a shorter period of illness.

Unfortunately, flu represents a diagnostic challenge. The clinical symptoms cannot be distinguished from those of other common canine respiratory diseases such as bordetella bronchiseptica, parainfluenza, respiratory coronavirus, and distemper virus.

Further, there are no point-of-care tests currently available to veterinarians. Unlike in human medicine, where a quick bedside test can be conducted to diagnose flu, testing for canine flu can be difficult. Careful specimen collection and handling is essential, and tests must be sent to outside laboratories. Due to the expense and difficulty of this, often canine influenza is not definitively diagnosed; instead, it’s treated like other canine respiratory diseases.

How to Treat Dog Flu

There isn’t a specific treatment for dog flu; rather, general supportive care is given, especially if your dog is only mildly affected.

If your dog has more severe symptoms or evidence of pneumonia, he may be treated in the hospital with antibiotics (in case of secondary bacterial infection), intravenous or subcutaneous fluids, oxygen therapy, and fever-lowering NSAIDs. Your dog may also be isolated in a low-stress environment to prevent further spread and to help minimize his anxiety.

Canine Influenza Transmission

Influenza is highly contagious and spreads rapidly in social situations. Transmission is via aerosolized droplets (coughing, sneezing) and direct contact. It can also be spread on contaminated objects such as food or water bowls, leashes, and kennels. The flu virus can live up to 48 hours on these surfaces, so proper disinfection is a critical part of prevention.

dog show influenza risk

Places where dogs congregate, such as dog shows and dog-sports events, boarding and training facilities, and dogs parks, pose a greater risk of influenza transmission. Note that there is no “flu season” for the canine flu; it can infect your dog at any time of the year.

The most common places for a dog to catch the flu virus include dog parks, grooming facilities, kennels, and daycares.

Dog Flu Vaccines

Could you have prevented your dog from contracting the flu? There are vaccines available that protect against both strains. All of the canine influenza vaccines contain killed viruses.

As with the human influenza vaccine, it is important to remember that the flu vaccine doesn’t always prevent your dog from getting sick. In the event that he does contract the flu, the vaccine helps lessen the duration and severity of symptoms, including pneumonia and lung lesions. Dogs who were vaccinated against the flu but still transmitted the disease will shed the virus into their surroundings for a shorter period of time than unvaccinated dogs.

Side effects of the vaccine are uncommon and generally similar to other vaccine reactions: lethargy, low-grade fever, a lump at the site of injection, hives, and itching. In very rare cases, severe reactions can occur.

Pregnant dogs should not be vaccinated against the flu.

The influenza vaccination has been described by the American Veterinary Medical Association as a “lifestyle” vaccination, not a “core” vaccine (core vaccines are recommended for all dogs). A lifestyle vaccine is recommended for dogs who are at a higher risk due to their increased exposure to other dogs – such as dogs who attend daycare, boarding, or group classes, or frequent dog parks or dog shows. The first vaccine can be given as early as six weeks of age, and in all cases, it is critical that a booster is received two to four weeks later.

puppy with dog flu

Puppies and immune-compromised dogs can quickly progress from a minor case of the flu to pneumonia, and require emergency veterinary care if they are to have any hope of recovery. Intravenous fluids, antibiotics, and fever-relieving NSAID medication pulled this puppy with pneumonia through.

Don’t wait until a few days before boarding to get the vaccine. The dog should not be considered protected from disease until two weeks after his second vaccination. After the initial series, the flu shot is given annually.

If your dog is not in social situations or flu has not been reported in your state, the flu vaccine is not necessary. If you’re uncertain whether your dog should receive the vaccine, your veterinarian can help guide you.

Want more information on vaccination protocols for dogs? Find it here.


Overall, while canine influenza can be serious, in most cases the symptoms are mild and self-limiting. Even in severe cases, the mortality rate is low – but some dogs do die from the illness. Vaccination is very effective and should be pursued for dogs in highly social environments.

Catherine Ashe graduated the University of Tennessee College of Veterinary Medicine in 2008. After a small-animal intensive emergency internship, she has practiced ER medicine for nine years. She is now working as a relief veterinarian in Asheville, North Carolina, and loves the GP side of medicine. In her spare time, she spends time with her family, reads voraciously, and enjoys the mountain lifestyle.

Comments (6)

I agree with the posting above, I'm 60 yrs old and never had the flu shot... why would I give it to my healthy dog. I work hard (for both my dog and my family) at eating the right foods and taking supplements to build our immunities strong to fight any illnesses. I think that this scare tactic is just another ploy from Big Pharma to keep us in a state of needing them... they have no cures, just treatments to line their pockets. They don't make money suggesting to eat healthier. I agree that if you don't take care of yourself (pets included) that maybe these shots would help lessen the symptoms... however there are many drawbacks to consider...these vaccines are not my choice. Just my 2 cents.

Posted by: ANNIEO | October 18, 2018 10:46 AM    Report this comment

My dogs participate in a number of different dog events. After two unknowingly brought the H2N3 home from a show last May, I will keep my dogs vaccinated. My entire household was very sick within 3 days, including a 13-year-old and a pregnant bitch a week away from whelping. It was very frightening and NOT an experience I care to repeat.

Posted by: imacorgimim | June 25, 2018 9:40 AM    Report this comment

Ping, I have wondered the same thing. Immunity from most viral vaccines, such as for Parvo and Distemper, lasts at least three years and likely for the lifetime of the dog, while most bacterial vaccines, such as for leptospirosis and bordetella, must be repeated yearly. Canine Influenza is a virus, yet they're telling us this vaccine needs to be given yearly. I don't understand why, but the Merck press release announcing the vaccine included this quote from Dr. Ronald Schultz, who spearheaded the movement to stop unnecessary annual revaccinations and so I consider him a reliable source:
"Dogs at risk for CIRDC (canine infectious respiratory disease complex) should be vaccinated at least yearly with both influenza strains, H3N8 and H3N2, in addition to the other causes of 'Canine Cough',” said Ronald Schultz, Ph.D., professor of pathobiological sciences at the University of Wisconsin School of Veterinary Medicine. “The occurrence of one strain or the other is unpredictable and so dogs should be protected against both. Because dogs do not maintain long duration of immunity against influenza, it is important to vaccinate them annually.”
This may have to do with the vaccines using a killed (rather than modified live) virus, or something else entirely. I have not been able to find out more despite intensive searching.

Posted by: Mary Straus | June 24, 2018 2:02 PM    Report this comment

The same questions about the human flu vaccine apply to the dog flu vaccine. After reading the facts in this article, why would I vaccinate my dog? I have never had a flu vaccine, nor has my elderly family members. The renown physician, Dr. Christiane Northrop, has advised that to be healthy that we should focus on building immunity, not obsess on diseases.

Posted by: Czerny | June 24, 2018 11:12 AM    Report this comment

I have the million dollar question. Once the dog receives the initial series, why must it recieve a yearly booster providing the vaccine is the same and not for a mutated virus? No one has been able to answer this, and it can't be titered because if it's still in thier system it would count against the serology numbers as an active infection. This is not a virus I want to play with, so i did the yearly booster, but my gut says it's not necessary.

Posted by: Ping | June 24, 2018 10:25 AM    Report this comment

My dog Norman was really sick last year and I helped him get better quickly with a bone broth tea. You can make it at home yourself, but to save the trouble I purchased a product called busters brew which has only safe and natural ingredients and no fillers. It smells so good that I wanted some for myself. :)

Posted by: Josh | June 22, 2018 3:22 PM    Report this comment

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