As canine flu causes another (and particularly impressive) round of outbreaks in the US, a lot of questions arise. A big one involves vaccination.
I won’t go over the whole “what is canine flu?” spiel in this post, but I’ll give a quick overview of why we care about it. It’s a highly transmissible virus that acts… well… like flu does in people. It can cause disease in dogs ranging from mild to fatal. The mortality rate is hard to estimate but it’s probably 1-2%. It was ~2% in our Canadian outbreak of canine influenza in 2018 and we had really intensive surveillance, so it’s probably a pretty accurate number. Deaths are most often reported in older dogs. Dogs with underlying heart or lung disease are presumably at higher risk for mortality too. The same might apply to brachycephalic breeds (squishy faced breeds like bulldogs) since they are more prone to respiratory complications. Like human flu, deaths in otherwise healthy, younger individuals are rare but can occur.
Flu outbreaks are a big problem, and that can be a bigger issue in dogs than people, because we don’t have the same degree of seasonal flu every year in dogs. In humans, there’s a lot more population immunity because of repeated exposure and vaccination. Most dogs in North America have neither been exposed nor infected, so they’re ripe-for-the-picking immunologically.
Obviously there’s a canine flu vaccine, since that the topic du jour…
Yes, we have a couple of canine flu vaccines. They can be for the H3N2 strain alone, or H3N2 and H3N8. H3N2 is the currently circulating canine flu strain. It’s an avian-origin strain that has become adapted to dogs and entered the US from Asia in 2015 (and repeatedly thereafter). H3N8 canine flu emerged in the early 2000s, but as far as we can tell, it hasn’t been around for a while. So, H3N2 vaccination is the key.
How good is the canine flu vaccine?
Well, it’s a flu vaccine. They’re not known for being incredibly effective, but are useful to reduce the incidence and severity of disease. I’m most motivated to have higher risk dogs (e.g. old dogs, dogs with other health problems) vaccinated to reduce the risk of them getting severe disease. It’s going to be less effective as a population control measure since it isn’t great for protection against viral shedding, but it should help some.
What dogs should be routinely vaccinated against flu?
That’s a tough call since it’s a really sporadic disease. You might not have flu within 100 km of your dog for its entire life, or you might run into an infected dog tomorrow.
My main considerations are risk of exposure and risk of severe disease.
- Risk of exposure depends on whether the virus is in the area, how likely it is that it will be brought into the area (e.g. outbreaks nearby), how likely it is for the dog to be exposed somewhere else (e.g. the dog travels with its owner or goes to dog shows), how likely it is for the dog to be exposed to a high risk dog from somewhere else (e.g. contact with dogs imported from Asia, or dogs from other areas where flu is active) and how many dog contacts it has (the more contacts, the greater the risk, particularly if there are contacts with dogs of unknown health and travel status).
- Risk of severe disease is the other consideration, as described above. I’m quicker to recommend any respiratory disease vaccine in seniors, dogs with other illnesses and brachycephalics.
Thinking about those two components helps assess how useful the vaccine might be.
If flu is active in your area, vaccination is definitely worth talking about with your veterinarian.
How is canine flu vaccine given, and how often?
It’s an injectable vaccine. It requires an initial dose and then a booster 2-4 weeks later. That booster is important and shouldn’t be missed. We don’t do that in people, but dogs need it since most don’t have pre-existing immunity from earlier exposure and vaccination. After that initial series, it’s boosted once a year.
Another potential issue is vaccine availability. It’s been a niche vaccine, but with the large number of outbreaks in the US at the moment, demand has outpaced supply. Shortages are currently an issue in many areas.
While not related to the vaccination theme of today’s post, the question of whether canine influenza poses a risk to people often comes up too.
As far as we know, currently circulating canine flu strains do not infect people. That doesn’t mean it’s impossible (the current H3N2 changed from a bird to canine flu virus) but there’s no evidence it’s a concern right now. The main concern is the potential for a recombination, where different flu viruses (e.g. human, avian, swine, canine) infect the same host and the same time, and then reassort and create a new flu virus. We don’t have evidence of this happening but it’s always a concern with flu viruses, and it’s why we try to limit the number of different flu viruses in circulation (in any species).
At this point, we don’t have any evidence of canine flu in Canada. It might occur any time, and who knows where it will pop up, but at this point, the risk of infected dogs in my area is low.
Beyond that, Ozzie and Merlin don’t’ have particularly busy social calendars. We live in the country and they don’t see other dogs here. They see a small number of family members’ dogs sporadically, but their overall dog contacts are limited.
Ozzie (pictured here) is young and probably at limited risk of severe disease.
Merlin’s 11 and has chronic lymphoid leukemia that we’ve been managing for a year. He’s pretty healthy, but presumably at higher risk of a complication.
If flu was in the area, I might vaccinate them, but their risk of exposure is still pretty low so I’m not sure I would. If they had more contacts, I’d vaccinate Merlin for sure, and probably Ozzie too. With no flu in the area and limited dog contacts, I’m not motivated to vaccinate them at the moment. For some dogs, though, vaccination is definitely worth considering.
And from a non-canine standpoint… get your own flu shot. It won’t protect you or your dog from canine flu, but it’s been a nasty human flu season, and it can definitely help with that.