Each year, researchers select three influenza strains to include in the seasonal flu vaccine. Because there are so many different strains of the influenza virus, and because it mutates so rapidly, this selection is always a guess—a highly educated one based on global surveillance data, but still a guess.
In some years, the selections turn out to be remarkably accurate. During the 2010-2011 flu season, for example, the three strains selected for the seasonal flu vaccine were a very good match to strains circulating in the wild. In other years, however, researchers haven’t been so lucky. And since immunity to one strain of the flu doesn’t necessarily provide protection against other strains, a poor match between the vaccine strains and the circulating ones may mean an ineffective flu vaccine.
Researchers have long hoped to develop a so-called “universal” flu vaccine: one that could provide protection against all, or at least most, of the many strains of influenza capable of making people sick. If such a vaccine could be developed, the need for a new seasonal shot every year could be a thing of the past. More