For canine flu, it isn't a summer problem. A major outbreak started in California December 27th, 2017, and spread into Nevada, Idaho, and Oregon. It likely is more places than we think, because it isn’t always confirmed by lab data. Lack of confirmation is often because the pet owner declines the $200 test because treatment is symptomatic only, and by the time results are returned, their dog should be responding to treatment. It usually spreads in concentrations of dogs – boarding kennels, dog parks, day care, and obedience classes.
There are two major strains of canine influenza in the US: H3N2 and H3N8. There are vaccines available for either, or a bivalent vaccine that covers both strains (most common). A vaccinated dog can still get sick, and can still transmit the disease, although should have milder symptoms for a shorter period of time.
Yes, a strain of influenza may mutate, but these two canine-specific strains at this time don’t appear to be contagious to people.
[1] American Veterinary Medical Association
Footnotes
[1] https://www.avma.org/KB/Resources/FAQs/Pages/Control-of-Canine-Influenza-in-Dogs.aspx