. >> reporter: brad kersey was a family man, a father of four and just 37 years old when he got the flu. >> the amazing thing about this was just the speed with which everything occurred. >> reporter: mark kersey says his brother checked into the hospital in january, he died nine days later. >> by the time i was able to fly across the country, i you, unfortunately, never got to see him again before he passed away. >> reporter: the flu is usually the most dangerous for the very old and the very young. this season is different. according to the centers for disease control, 61% of those hospitalized are between 18 and 64 years old. about 90% of flu cases are caused high the h1 n1 strain of the virus. >> this is a little curious and it's the first time we've seen this pattern since 2009 when this virus last circulated. >> reporter: dr. joseph bresee is an epidemiologist at the c.d.c. he says the current vaccine covers h1 n1 and is about 60% effective if you get the shot. >> this group, the non-elderly adult population, is the least likely population to be vaccinated every year because as ad