the actual protection offered has been significantly lower than the medical community and the public believed. This has been particularly true for individuals over sixty-five years of age—the cohort of the population most vulnerable to seasonal influenza. We have too few good studies to determine the effectiveness in older people, but we found, on average, the vaccine works about 59 percent of the time in protecting younger adults. In some years it’s much less effective than that. For example, for the H3N2 strain, the 2014–15 vaccine actually provided 0 percent protection.
