Are "flu shots" cumulative?

[August_West]

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?

Thanks.

[USCDiver]

According to the CDC

If I got the flu or the flu vaccine last year, will I have immunity against the flu this year?
Not necessarily. Several studies conducted over different flu seasons and involving different influenza viruses and types of flu vaccine have shown that a person’s protective antibody against influenza viruses declines over the course of a year after vaccination and infection, particularly in the elderly. So, a flu shot given during one season, or an infection acquired in one season, may not provide adequate protection through later seasons.

The decline in protective antibody against the flu that occurs after vaccination or after flu infection may be influenced by several factors, including a person’s age, the antigen used in the vaccine, and the person’s health situation (for example, chronic health conditions that weaken the immune system may have an impact).

This decline in protective antibody has the potential to leave some people more vulnerable to infection, illness and possibly serious complications from the same influenza viruses a year after being vaccinated or infected.

So, for optimal protection against influenza, annual vaccination is recommended regardless of past vaccination status or flu infection.

[engineer_comp_geek]

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.