It's easy to never get the flu! When you start getting sick, just call it a cold. Done!
Seriously, though, the two have been confused so often that I don't think there's any difference any more - at least outside of a doctor's office….
I agree that there is some confusion in the public regarding influenza vs the common cold.
From a medical POV, it's in principle fairly simple. By definition, influenza is a disease caused by an influenza-virus, while the common cold is caused by a whole lotta … other viruses.
Clinically, influenza is usually a more severe disease, with general symptoms like fever (may be high (313K)), significant general feeling of sickness, and quite often muscular pain, compared to the common cold which as a rule have mostly local symptoms with little or only light general affection. So if coughing and sneezing and a running nose are your only symptoms, most likely it's not influenza. It's not water-tight, however. Back in my (*shivers*) doctor days, we had to report the number of different infections we encountered every week, for influenza the choice was "infections similar to influenza". To be sure, we had to identify the virus in a blood sample, which we seldom did (no need for it). Perhaps there are quick tests available now, I don't know.
Another important issue is that influenza has a higher risk of rather serious complications, which is why a yearly flu shot is recommended for the elderly (65 years+), people with chronic diseases (especially respiratory disesases) and - mostly for practical reasonss methinks, people who in their work are in contact with a lot of patients.
OK, somewhat off-topic, but I think the OP deliberately played with the doubloe meanings of "Flu".
a pibbur who has yet to take his shot (it currently rests in his refrigerator).
PS. The sloth isn't too far-fetched in his "treatment" suggestion. I once read a book, suggesting the following cure for the common cold. Go outside, be sure to get wet and cold. Then you will develop pneumonia, which unlike viral infections, can be treaated by antibiotics. The author may have been joking (it was a funny book) and he wasn't a health care professional. His name is Kjell Aukrust. DS.
PPS. There is a bacterium, Hemophilus influenza, which despite the name, has nothing to do with the flu. It causes infection of the throat in children, and occasionally it causes meningitis. DS.