Three-Quarters of People Who Got Flu Shot This Year Weren't Protected Against Most Common Strain

Data from the Centers for Disease Control and Prevention (CDC) published in the Morbidity and Mortality Weekly Report estimates 75 percent of people vaccinated for the flu this year were not protected against the H3N2 strain responsible for most infections in the current season, reports STAT . The vaccine was more effective against influenza B and H1N1 viruses, but only about 8 percent of people who tested positive this season were infected with strains from the influenza A family. "We are a bit concerned that the performance of the vaccine right now might reduce interest in getting vaccinated in the future," says Acting CDC Director Dr. Anne Schuchat. "But we have the other side that flu was just so bad so far this season, so many people have been sick and see how miserable it is." A previous study analyzing H3N2 protection over a number of years determined the vaccine's average effectiveness was about 32 percent or 33 percent. The CDC report says the H3N2 vaccine performance was less effective in older adults compared to children. Seniors aged 65 and up saw their risk of needing medical care for flu lowered by 17 percent, and in adults 50 to 64 the H3N2 component's efficacy was only 10 percent. Possible contributing factors to the vaccine's low effectiveness against H3N2 include mutations that occur in vaccine viruses when they are cultured in eggs.