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SARS-CoV-2 infected persons without symptoms can also infect others

Early data from China suggested that people without symptoms could infect others.(6) To better understand the role of transmission from infected people without symptoms, it is important to distinguish between transmission from people who are infected who never develop symptoms(75) (asymptomatic transmission) and transmission from people who are infected but have not developed symptoms yet (pre-symptomatic transmission). This distinction is important when developing public health strategies to control transmission.

The extent of truly asymptomatic infection in the community remains unknown. The proportion of people whose infection is asymptomatic likely varies with age due to the increasing prevalence of underlying conditions in older age groups (and thus increasing risk of developing severe disease with increasing age), and studies that show that children are less likely to show clinical symptoms compared to adults.(76) Early studies from the United States (77) and China (78) reported that many cases were asymptomatic, based on the lack of symptoms at the time of testing; however, 75-100% of these people later developed symptoms. A recent systematic review estimated that the proportion of truly asymptomatic cases ranges from 6% to 41%, with a pooled estimate of 16% (12%20%).(79) However, all studies included in this systematic review have important limitations.(79) For example, some studies did not clearly describe how they followed up with persons who were asymptomatic at the time of testing to ascertain if they ever developed symptoms, and others defined "asymptomatic" very narrowly as persons who never developed fever or respiratory symptoms, rather than as those who did not develop any symptoms at all.(76, 80) A recent study from China that clearly and appropriately defined asymptomatic infections suggests that the proportion of infected people who never developed symptoms was 23%.(81)

Multiple studies have shown that people infect others before they themselves became ill, (10, 42, 69, 82, 83) which is supported by available viral shedding data (see above). One study of transmission in Singapore reported that 6.4% of secondary cases resulted from pre-symptomatic transmission.(73) One modelling study, that inferred the date of transmission based on the estimated serial interval and incubation period, estimated that up to 44% (25-69%) of transmission may have occurred just before symptoms appeared.(62) It remains unclear why the magnitude of estimates from modelling studies differs from available empirical data.

Transmission from infected people without symptoms is difficult to study. However, information can be gathered from detailed contact tracing efforts, as well as epidemiologic investigations among cases and contacts. Information from contact tracing efforts reported to WHO by Member States, available transmission studies and a recent pre-print systematic reviews suggests that individuals without symptoms are less likely to transmit the virus than those who develop symptoms.(10, 81, 84, 85) Four individual studies from Brunei, Guangzhou China, Taiwan China and the Republic of Korea found that between 0% and 2.2% of people with asymptomatic infection infected anyone else, compared to 0.8%-15.4% of people with symptoms.(10, 72, 86, 87)

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https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions

Some good studies noted in this article that show how asymptomatic people can spread the virus.

Up to 2.2% asymptomatic spread is almost a rounding error and not definitive at all, imho.

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Four individual studies from Brunei, Guangzhou China, Taiwan China and the Republic of Korea found that between 0% and 2.2% of people with asymptomatic infection infected anyone else, compared to 0.8%-15.4% of people with symptoms.

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Things that caught my eye immediately.

Between 0 and 2.2%? That means it is as likely to be 0 as it is 2.2%, so 1%?

0.8-15.4% is a wide range, almost like what did we really learn.

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Four individual studies from Brunei, Guangzhou China, Taiwan China and the Republic of Korea found that between 0% and 2.2% of people with asymptomatic infection infected anyone else, compared to 0.8%-15.4% of people with symptoms.

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Asymptomatics are not drivers of the epidemic.

Or we could listen to Dr. Fauci.

Or there is this, if you like to lend weight to Chinese studies.

zebros_95 said:

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Up to 2.2% asymptomatic spread is almost a rounding error and not definitive at all, imho.

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That transmission rate is for asymptomatic people that never developed symptoms. There are other studies referenced in the article that show the asymptomatic transmission rate for people that turn symptomatic to be much higher.

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We report temporal patterns of viral shedding in 94 patients with laboratory-confirmed COVID-19 and modeled COVID-19 infectiousness profiles from a separate sample of 77 infectorinfectee transmission pairs. We observed the highest viral load in throat swabs at the time of symptom onset, and inferred that infectiousness peaked on or before symptom onset. We estimated that 44% (95% confidence interval, 3057%) of secondary cases were infected during the index cases' presymptomatic stage, in settings with substantial household clustering, active case finding and quarantine outside the home. Disease control measures should be adjusted to account for probable substantial presymptomatic transmission.

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P.U.T.U said:

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Or for a real world scenario 4 of my coworkers went to a skeet shooting challenge that a customer was holding and we found out yesterday there was a positive case. I know at least 20 other people plus my 4 coworkers were tested and all were negative. The event was outdoors only

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Can we all agree that if you are outdoors and there is a breeze and you don't stand in a concentrated group for extended periods of time, there is a low probability that you will transmit or become infected. I don't see how there can be a high enough concentration of the virus in an open air environment under such conditions.

Now, standing shoulder to shoulder in a crowd for more than 30 minutes, then yes, the risk goes up, especially if there is no breeze.

Keegan99 said:

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Four individual studies from Brunei, Guangzhou China, Taiwan China and the Republic of Korea found that between 0% and 2.2% of people with asymptomatic infection infected anyone else, compared to 0.8%-15.4% of people with symptoms.

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Asymptomatics are not drivers of the epidemic.

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'Superspreading' Events are and asymptomatic or pre-symptomatic carriers are undoubtedly a part of that phenomenon.

Undoubtedly?

GAC06 said:

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Undoubtedly?

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Yep. We knew very early on that this was going to be a bad one because people could spread the virus before they showed any symptoms.

01/31/20 - 'There's no doubt': Top US infectious disease doctor says Wuhan coronavirus can spread even when people have no symptoms

I think the confusion that a lot of people can't get around is the difference between Asymptomatic, Presymptomatic, and Paucisymptomatic.

Presymptomatic= no symptoms, but you're about to have them. You can spread it to others, especially in the days right before you develop symptoms. To what degree compared to a symptomatic patient is being studied and debated. This is thought to be the major reason COVID-19 is spread so readily...people spreading to others before they know they have it.

Asymptomatic= you test positive for and are carrying the virus, but have absolutely no symptoms and never will. These people are thought to not spread the virus to others very readily at all. Obviously, without follow up several weeks later, there may be some difficulty differentiating true asymptomatic carriers from presymptomatic...because until you do or do not develop symptoms, you have no idea which category you fit into.

Paucisymptomatic= You have very mild symptoms that might be confused with allergies or a mild cold. My understanding is you can spread to others, but I am not sure to what degree relative to fully symptomatic vs. asymptomatic vs. presymptomatic.

beerad12man said:

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etxag02 said:

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GAC06 said:

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Undoubtedly?

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Yep. We knew very early on that this was going to be a bad one because people could spread the virus before they showed any symptoms.

01/31/20 - 'There's no doubt': Top US infectious disease doctor says Wuhan coronavirus can spread even when people have no symptoms

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We do not "know" that undoubtedly. In fact, many prominent people have come out with different opinions since then. Probably need to link something past 1/31/20 for updated data.

From the original post above --Multiple studies have shown that people infect others before they themselves became ill, (10, 42, 69, 82, 83) which is supported by available viral shedding data (see above).

Now, my guess is plenty confuse completely asymptomatic with minor symptoms one might think are just allergies. But truly asymptomatic? There are a lot of people that think the spread is a minimal part of the equation and it's most certainly not "undoubtedly". Or pre symptomatic versus asymptomatic. I don't think they've proven it either way.

If you read my statement, I did say "before they showed any symptoms". I get your point and partly agree. I would not say they are a minimal part based on the evidence we have collected to date. 'Truly asymptomatic', as you put it, transmission is difficult to study without widespread, thorough contact tracing (including genetic sequencing) which we don't really have in America.

Edit: Randy seemed to touch on everything I did with better detail. Thanks

Yep. He did a good job defining terms to move the conversation along. Many people are conflating multiple, nuanced aspects of this virus to push a narrative.

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DadHammer said:

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Four individual studies from Brunei, Guangzhou China, Taiwan China and the Republic of Korea found that between 0% and 2.2% of people with asymptomatic infection infected anyone else, compared to 0.8%-15.4% of people with symptoms.(10, 72, 86, 87)

You are worried about the 0 - 2.2% ???

Good Grief man, its like you are reaching as hard as possible for any and i mean any bad news you can find. Why?

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Are you being deliberately obtuse? You seem to be pushing a narrative.

That percentage is for asymptomatic people that do not develop symptoms.

You then have people who are infected, asymptomatic and contagious prior to presenting symptoms. There is much evidence (see studies referenced in the OP) that indicate that infectiousness peaks before symptom onset when people are still asymptomatic.

GE said:

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Jmiller said:

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No, before the onset of symptoms. Breathing wouldn't distribute as much of the virus as talking or singing. Then combine with other factors like environmental, social distance, number of people around, etc. and the odds of transmission increase.

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I don't get the talking/singing thing at all, other than for a specific subset of people who close talk and spit on their friends. I just held my hand in front of my mouth and breathed normally. Then yelled, sang, and talked normally. No noticeable increase air flow hitting my hand in the yelling singing and talking compared with just breathing.

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Signing, if you do it properly and projecting, involves deeper breaths and exhalations. Sampling deeper into the lungs probably increases viral load.

A soloist or chorus singing for an audience is probably pretty different from the way a lot of the congregation sings at church or party goers sing happy birthday.

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"One-fifth of the asymptomatic patients and roughly half of the symptomatic patients were still passing on the SARS-CoV-2 virus three weeks after initial infection though this did not directly reflect their contagiousness."

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So nothing about actual transmission?