The Centers for Disease Control and Prevention says that next season's flu shot, available in the fall, will contain two strains of the virus that were not present in last year's shot, which was not very effective at preventing the illness.
According to the new CDC report people who got last season's flu shot were just 19 percent less likely to visit their doctor for the flu. This marked a huge drop off compared to a 56 percent reduction in medical visits among those who got the shot during the 2012 to 2013 season.
While most of the flu viruses that circulated last fall were of the H3N2 strain, about 80 percent of the H3N2 viruses in circulation were different from strains included in the 2014 to 2015 shots.
To fix to this mismatch, officials plan to switch one of the strains in next year's trivalent flu shot and two of the strains in the quadrivalent flu shot. The trivalent shot protects against two influenza A strains, H1N1 and H3N2, and one influenza B strain. The quadrivalent protects against an extra influenza B virus.
Last flu season had the highest rate of hospitalizations for older adults in a decade, the CDC said, at 322 per 100,000 among U.S. adults age 65 and older. The previous high for this age group was 183 per 100,000 during the 2012 to 2013 season, a sign that vaccination is increasingly important among this demographic.