There would be two vaccinations that could be referred to as "flu" vaccines. One is canine parainfluenza which is a standard fraction of most "5 Way" and "7 Way vaccinations that are given to puppies and then boosted as adults. The second in canine influenza which has been around about 10 years and is considered endemic meaning there are areas of the country that have much higher incidence, Florida is one of those areas. I would rely are your vets recommendations as they are most familar with the risks in your locale. As with many vaccine if your dog is going to mingle with a variety of other dogs like boarding, classes or pubblic parks the justification for vaccination is stronger.