Most vaccines only need to be administered once or a few times in a person's life. But the flu mutates so frequently that there are constant updates to the vaccine based on what the World Health Organization recommends. That's why many people get flu shots every winter.
But researchers at vaccine-maker Sanofi are getting closer to a universal vaccine that might provide broader protection against the flu. That way, instead of a shot once every year, the vaccine could broadly protect against the virus even as it evolves over the course of a few years.
Today's flu vaccines have either three or four strains in one shot, and newer vaccines could cover those in a broader way. Rather than be specific to one bug, the vaccines against those strains could be general enough to face off against any mutation the virus takes. If you're able to have broad vaccines that protect against the different flu subtypes, you could ideally just use whichever one makes the most sense in a given outbreak.
The idea's still in the pre-clinical phase.