# How long is a person with influenza infectious?

**URL:** <https://boards.straightdope.com/t/how-long-is-a-person-with-influenza-infectious/518140>\
**Category:** Factual Questions\
**Created:** [November 19, 2009, 11:46am UTC](https://boards.straightdope.com/t/how-long-is-a-person-with-influenza-infectious/518140 "2009-11-19T11:46:16Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mr.jp](https://avatars.discourse-cdn.com/v4/letter/m/48db29/32.png) [@mr.jp](https://boards.straightdope.com/u/mr.jp)\
**Post date:** [November 19, 2009, 11:46am UTC](https://boards.straightdope.com/t/how-long-is-a-person-with-influenza-infectious/518140/1 "2009-11-19T11:46:16Z")

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After the fever is gone, and the person feels well, is he still infectious? If so, for how long?

This seems like a fact that should be widely known, but noone here does for sure.

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**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\
**Post date:** [November 19, 2009, 12:47pm UTC](https://boards.straightdope.com/t/how-long-is-a-person-with-influenza-infectious/518140/2 "2009-11-19T12:47:32Z")

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When is a person with influenza contagious/infectios? A person is most likely to pass on the virus beginning one to two days before the onset of symptoms and ending four to five days after the onset of symptoms.

From CDC and various sources.

Note that is it a guideline, based on averages. In poor health and can’t beat the infection fast? It could be longer after the onset of symptoms.

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**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\
**Post date:** [November 19, 2009, 1:36pm UTC](https://boards.straightdope.com/t/how-long-is-a-person-with-influenza-infectious/518140/3 "2009-11-19T13:36:46Z")

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Newer information about H1N1 (swine flu) indicates that people can still be infectious for several days after they are apparently over it. In particular, people can be infectious even three days after their last bout of fever.