# How fast for an infected person to become contagious? **URL:** \ **Category:** The Quarantine Zone\ **Tags:** covid-quarantine\ **Created:** [June 17, 2020, 6:44am UTC](https://boards.straightdope.com/t/how-fast-for-an-infected-person-to-become-contagious/855833 "2020-06-17T06:44:45Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [June 17, 2020, 6:44am UTC](https://boards.straightdope.com/t/how-fast-for-an-infected-person-to-become-contagious/855833/1 "2020-06-17T06:44:45Z")
I haven’t read this info yet, but suppose Person A infects Person B. How long does it take for Person B to become truly infected (that is, from the moment the virus enters his body, to truly taking up host and propagating,) and how long before Person B becomes infectious to other people in his own right? 12 hours, 36 hours? ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [June 17, 2020, 8:56am UTC](https://boards.straightdope.com/t/how-fast-for-an-infected-person-to-become-contagious/855833/2 "2020-06-17T08:56:34Z")
Three to fourteen days incubation time. Source: the Coursera course we took to be contract tracers as need be. (We aren’t doing it but the baseline quantity of people _able_ to was a prerequisite for the state of NY to go to the next reopening phase) ETA: that’s how long between catching it and developing any symptoms. There is a TWO DAY WINDOW between the time Person B becomes infectious (which happens FIRST) and the time when Person B gets any SYMPTOMS. ---
**Author:** ![Mops](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mops/32/16494_2.png) [@Mops](https://boards.straightdope.com/u/Mops)\ **Post date:** [June 17, 2020, 10:55am UTC](https://boards.straightdope.com/t/how-fast-for-an-infected-person-to-become-contagious/855833/3 "2020-06-17T10:55:54Z")
So that would be 1 to 12 days from being infected to being infectious, for those who do go on to develop symptoms? ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [June 17, 2020, 5:20pm UTC](https://boards.straightdope.com/t/how-fast-for-an-infected-person-to-become-contagious/855833/4 "2020-06-17T17:20:25Z")
Thanks. How long, after the virus takes hold in someone’s body, does a nasal swab test become able to detect it? also, **AHunter3** , so this means an infected person becomes contagious very rapidly, within hours, even though asymptomatic? ---
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [June 17, 2020, 7:53pm UTC](https://boards.straightdope.com/t/how-fast-for-an-infected-person-to-become-contagious/855833/5 "2020-06-17T19:53:54Z")
> [@Velocity](#): > > Thanks. > > How long, after the virus takes hold in someone’s body, does a nasal swab test become able to detect it? 2-3 days. Source, that was what I was told when we were representing repatriated citizens, they had to be detained at least 48 hours after arrival and then tested. This was back in April and one of the Doctors I dealt with told me he didn’t think asymptomatic transmission was a thing and he doubted many were actually truly asymptomatic. I just politely nodded and rolled my eyes then, turns out he was right. ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [June 18, 2020, 3:59am UTC](https://boards.straightdope.com/t/how-fast-for-an-infected-person-to-become-contagious/855833/6 "2020-06-18T03:59:55Z")
> [@Velocity](#): > > Thanks. > > How long, after the virus takes hold in someone’s body, does a nasal swab test become able to detect it? > > also, **AHunter3** , so this means an infected person becomes contagious very rapidly, within hours, even though asymptomatic? No… sorry, I found it a little confusing myself on 1st take. Day 1: Person B inhales some virus particles by being too close to Person A Day 2: nothing Day 3: probably nothing Day 4 or Day 14 or anywhere in there: Person B’s incubation period is over and they are now shedding virus particles. Person C can get sick. But Person B has no symptoms yet Day After That: same shit. Infectious but no symptoms. Day After That: Person B is likely to be getting headaches and developing a cough Day After That: Person B is getting sicker, feverish etc. And Still quite infectious, by the way Day After That: same Day After That and so on: Eventually Person B’s symptoms are abating. Comes a day without any fever and reduced shortness of breath. Ten Days After No Fever / No Serious Symptoms: Person B may be assumed to no longer be infectious and can cease being in isolation.