Flu Vaccine Doing Mediocre Job in Preventing Illness Flu season rages on and the vaccine isn't doing a particularly good job of slowing it down. According to the CDC, this year's vaccine is 36 percent effective, meaning it reduces the number of doctor visits by 36 percent. It’s only 25 percent effective against the most common strain circulating this year, the H3N2 strain. When it came to children 8 and younger, the vaccine performed better, offering 59 percent protection against H3N2. To put that into perspective, three-quarters of the 63 children who have died of flu this season had not been vaccinated. “CDC continues to recommend influenza vaccination because the vaccine can still prevent some infections with currently circulating influenza viruses, which are expected to continue circulating for several weeks.