# Are "flu shots" cumulative?

**URL:** <https://boards.straightdope.com/t/are-flu-shots-cumulative/637536>\
**Category:** Factual Questions\
**Created:** [October 12, 2012, 5:39pm UTC](https://boards.straightdope.com/t/are-flu-shots-cumulative/637536 "2012-10-12T17:39:01Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![August\_West](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/august_west/32/18069_2.png) [@August\_West](https://boards.straightdope.com/u/August_West)\
**Post date:** [October 12, 2012, 5:39pm UTC](https://boards.straightdope.com/t/are-flu-shots-cumulative/637536/1 "2012-10-12T17:39:01Z")

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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.

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**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\
**Post date:** [October 12, 2012, 5:45pm UTC](https://boards.straightdope.com/t/are-flu-shots-cumulative/637536/2 "2012-10-12T17:45:52Z")

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According to the [CDC](http://www.cdc.gov/flu/about/qa/disease.htm)

> [@](#):
>
> **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.

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**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\
**Post date:** [October 12, 2012, 7:45pm UTC](https://boards.straightdope.com/t/are-flu-shots-cumulative/637536/3 "2012-10-12T19:45:52Z")

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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.