Flu infections are relatively rare. The majority of people who claim to have flu just have a bad cold, which is caused by a group of rhinoviruses that are not closely related to influenza virus. Persistent colds are associated with having a weak immune system.
I've only had flu once in my lifetime. Having gone to bed feeling just fine, I woke up aching all over so badly that I had to crawl to the bathroom to vomit. I felt like I was going to die and it was terrifying. My doctor advised me to stay in bed. A fever and relatively mild cold symptoms followed and disappeared after about 2 days.
The majority of under 50s have never had influenza virus.
F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.