Will Falconer, DVM Moderator
It doesn't, but no harm in getting a check up. Generally, sick dogs don't play, eat, eliminate normally, so based on that, so I don't hear a sick dog here.
Just beware that your best stance,if you go to a vet is "diagnostics only please," as it's all too common to dish out antibiotics if they feel you are concerned and want to "do something." Without a strong justification, those drugs impair the immune system unnecessarily, and you most certainly want your dog's immune system to be on full functioning alert.
(And flu is a virus, right? "Secondary bacteria" is a common excuse to throw antibiotics even at viruses, which they can't possibly kill.)