# Can illness "negate" a flu shot's effectiveness?

**URL:** <https://boards.straightdope.com/t/can-illness-negate-a-flu-shots-effectiveness/208819>\
**Category:** Factual Questions\
**Created:** [October 22, 2003, 1:45am UTC](https://boards.straightdope.com/t/can-illness-negate-a-flu-shots-effectiveness/208819 "2003-10-22T01:45:00Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![vivalostwages](https://avatars.discourse-cdn.com/v4/letter/v/d07c76/32.png) [@vivalostwages](https://boards.straightdope.com/u/vivalostwages)\
**Post date:** [October 22, 2003, 1:45am UTC](https://boards.straightdope.com/t/can-illness-negate-a-flu-shots-effectiveness/208819/1 "2003-10-22T01:45:00Z")

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I’m asking because of what the nurse said about 10 days ago when I got the flu shot: “Stay healthy, because this takes two weeks to become effective.”

Easier said than done. Everyone I know has the coughing, sneezing, nose-blowing mess going on these days, and I got it last week. Will the flu shot remain effective no matter what, or does it depend on the severity of an illness?

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**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\
**Post date:** [October 22, 2003, 5:48am UTC](https://boards.straightdope.com/t/can-illness-negate-a-flu-shots-effectiveness/208819/2 "2003-10-22T05:48:14Z")

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It will work no matter what, whether you get ill or not. What the nurse was saying is that you won’t be protected from the flu for about two weeks. So for the next two weeks, you can still get the flu. But whether you get sick or not, you’ll be protected after that.

Incidentally, I can’t verify that two week window she gave you. Maybe one of our resident docs will show up and confirm it.