How long before a COVID positive person can't transmit any more?

[Alfred001]

What is the latest evidence on how long it takes for a person who catches COVID to be no longer able to transmit the virus? I'm sure there's variability, but what's the upper limit of how long a person can be a transmitter?

[TheVat]

The standard has been ten days and 24 hours with no fever, if we are talking of mild or asymptomatic covid.   But isolation can be longer if the infection is severe or if the person is immunocompromised.   Here's the CDC page where you can scroll down a ways to see all the various scenarios:

https://www.cdc.gov/coronavirus/2019-ncov/your-health/quarantine-isolation.html

[iNow]

Technically, a person can always transmit and shed virus regardless of when they were last infected

[zapatos]

26 minutes ago, iNow said:

Technically, a person can always transmit and shed virus regardless of when they were last infected

So how does that work? Some (or all) people never completely rid themselves of the virus?

[CharonY]

As iNow mentioned, there could be weird issues, especially in folks with immune system problems, resulting in re-emergence of the disease. There was recently a of Ebola, where a person recovered but presented symptoms 6 months after. 

I do not recall having read something as long for COVID-19, but there were studies where folks where folks tested positive again after over 20 days of discharge. The issue is that one can really only distinguish between relapse and re-infection if the patients have been isolated but tested for that time frame.

 

[iNow]

22 minutes ago, zapatos said:

So how does that work? Some (or all) people never completely rid themselves of the virus?

More like even when their immune system is able to dispatch it, this cleaning process takes time. Much like being immunized... helps afford protection, but isn't some 100% shield. Walk into an ER... even vaccinated or recovered from infection... you'll pick up virus. Then walk into a grocery store after and you can infect someone else. 

[CharonY]

25 minutes ago, iNow said:

More like even when their immune system is able to dispatch it, this cleaning process takes time. Much like being immunized... helps afford protection, but isn't some 100% shield. Walk into an ER... even vaccinated or recovered from infection... you'll pick up virus. Then walk into a grocery store after and you can infect someone else. 

Note that if you are tested negative, it basically means that your viral titer has fallen to a level where it is unlikely that you are also infectious or present acute symptoms (excluding long-haul symptoms that is). A relapse happens if the virus regains a foothold again before being cleared entirely. It is not quite clear why this happened. In all documented cases I read folks also had antiviral treatment, but that could also be a coincidence as they were also the only folks being isolated and tested long enough to establishing a relapse.

[iNow]

46 minutes ago, CharonY said:

Note that if you are tested negative, it basically means that your viral titer has fallen to a level where it is unlikely that you are also infectious or present acute symptoms

Indeed and agreed. My basic thinking, however, is that at some time AFTER that test one might encounter someone infected, increase their viral load, and pass it on to others without knowing. In essence, my original comment was you're ALWAYS able to pass the virus to others even when you've bene previously infected or fully vaccinated, so bear that in mind when thinking through these issues. It's not like you're impenetrable after 10 days, for example. 

[CharonY]

1 hour ago, iNow said:

Indeed and agreed. My basic thinking, however, is that at some time AFTER that test one might encounter someone infected, increase their viral load, and pass it on to others without knowing. In essence, my original comment was you're ALWAYS able to pass the virus to others even when you've bene previously infected or fully vaccinated, so bear that in mind when thinking through these issues. It's not like you're impenetrable after 10 days, for example. 

Gotcha, I seem to have misinterpreted your post, my apologies. Based on OP I assumed the question was targeted at a singular infection event. That being said, unless there are some immune issues and assuming that there is not a different variant going around, typically after an infection (or after immunity has built up after vaccination) you have a high antibody titer that clears out new encountered viruses fairly efficiently. It takes a while until this protection drops.

[zapatos]

I'm trying to figure out what happened here.

My wife went out of town to visit our son, his wife and their two children aged 1 and 3. The three year old came in close contact with someone who had COVID while at daycare so all four in my son's family were tested, and came back positive for COVID the day after my wife arrived. My wife, son, and his wife are all vaccinated and boosted.

As the one year old was never masked and my wife couldn't maintain distance and masking in the presence of such an adorable grand daughter, all precautions were soon thrown to the wind by everyone and my wife spent two more days, indoors, no masks, no distancing, with four people who had COVID. None of the four had symptoms beyond what you would see from a typical winter illness.

My wife tested negative the day she came home (antigen test) and again five days later. Never had a hint of any symptoms.

How is it that my wife did not get COVID? Did the vaccine do that well? Might she have previously had it? I was shocked that she seems to have not contracted COVID.

 

[TheVat]

The antigen tests, especially where the omicron variant is concerned, has a lot of false negatives.  I am still unsure if the two week infection I just got over (covid like symptoms, much hacking, worst URI ever had) was covid or not, though both my antigen tests (spaced a couple days apart while very symptomatic, per the mfr. recommendation) were negative.  

You may never know.  And now some research suggests the nasal swab doesn't even work for omicron, and a throat swab is really needed because omicron will concentrate more in saliva and throat mucus rather than nose.  In the UK, they are recommending throat swabs now.  

 

[CharonY]

24 minutes ago, zapatos said:

I'm trying to figure out what happened here.

My wife went out of town to visit our son, his wife and their two children aged 1 and 3. The three year old came in close contact with someone who had COVID while at daycare so all four in my son's family were tested, and came back positive for COVID the day after my wife arrived. My wife, son, and his wife are all vaccinated and boosted.

As the one year old was never masked and my wife couldn't maintain distance and masking in the presence of such an adorable grand daughter, all precautions were soon thrown to the wind by everyone and my wife spent two more days, indoors, no masks, no distancing, with four people who had COVID. None of the four had symptoms beyond what you would see from a typical winter illness.

My wife tested negative the day she came home (antigen test) and again five days later. Never had a hint of any symptoms.

How is it that my wife did not get COVID? Did the vaccine do that well? Might she have previously had it? I was shocked that she seems to have not contracted COVID.

 

In addition to the test itself, there are no guarantees regarding spread. It depends a lot on the viral load in the infected individuals and there is evidence that in vaccinated folks the viral load is lower on average (though not consistently so) and the risk of a boosted individual to get infected is cut down roughly by half (on average, there is a lot of variability here, too). It is also possible that it was a different variant that they were exposed to, where the vaccination is even more effective against. The whole host-pathogen interaction is subject to many stochastic factors (also including innate immune responses) so it might be impossible to figure out what ultimately happened. But if I were to hazard a guess I would think that having several doses of the vaccine would have played a significant role in it.

 

[zapatos]

Further to our discussion, here is a recent study which discusses the likelihood of COVID spread within a household.

Quote

The probability for spreading within a household was 39% for BA.2 versus 29% for BA.1, the original omicron strain that was dominant worldwide as of Jan. 19, according to the World Health Organization.

https://www.cnbc.com/2022/01/31/the-new-omicron-subvariant-is-more-contagious-but-vaccinated-people-are-less-likely-to-spread-it-study-finds.html