Are "flu shots" cumulative?

It’s once again the time of year for flu immunizations and I was wondering if a person gets their flu shot every year, does it have a cumulative effect?

I know they vary the strains used in the shot each year, so I guess what I’m asking is if the shot 2 years ago contained, say, H3N2, am I immunized against that strain for life or do I need to get the flu shot each year that H3N2 is a possible infectious strain?


According to the CDC

The flu virus mutates fairly quickly. Vaccinations against any one strain are typically only good for a few years. After that, chances are that the virus has mutated too much for your antibodies to recognize it.