A link to the product label can be found here, as well as a summary of the recommendations for the use of the canine flu vaccine:
https://www.merck-animal-health-usa....Flu-Bivalent/1
When I google side effects for the vaccine, the only reputable site I've come up with so far is the AVMA general page for vaccine reactions:
https://www.avma.org/public/PetCare/...ccination.aspx
If I can find something more specific, I'll post it.