Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus

[brooklynite]

Source: Science

The novel coronavirus that emerged in Wuhan, China (SARS-CoV2) at the end of 2019 quickly spread to all Chinese provinces and, as of 1 March 2020, to 58 other countries (1, 2). Efforts to contain the virus are ongoing; however, given the many uncertainties regarding pathogen transmissibility and virulence, the effectiveness of these efforts is unknown.

The fraction of undocumented but infectious cases is a critical epidemiological characteristic that modulates the pandemic potential of an emergent respiratory virus (3–6). These undocumented infections often experience mild, limited or no symptoms and hence go unrecognized, and, depending on their contagiousness and numbers, can expose a far greater portion of the population to virus than would otherwise occur. Here, to assess the full epidemic potential of SARS-CoV2, we use a model-inference framework to estimate the contagiousness and proportion of undocumented infections in China during the weeks before and after the shutdown of travel in and out of Wuhan.

We developed a mathematical model that simulates the spatiotemporal dynamics of infections among 375 Chinese cities (see supplementary materials). In the model, we divided infections into two classes: (i) documented infected individuals with symptoms severe enough to be confirmed, i.e., observed infections; and (ii) undocumented infected individuals. These two classes of infection have separate rates of transmission: ?, the transmission rate due to documented infected individuals; and ??, the transmission rate due to undocumented individuals, which is ? reduced by a factor ?.

Spatial spread of SARS-CoV2 across cities is captured by the daily number of people traveling from city j to city i and a multiplicative factor. Specifically, daily numbers of travelers between 375 Chinese cities during the Spring Festival period (“Chunyun”) were derived from human mobility data collected by the Tencent Location-based Service during the 2018 Chunyun period (1 February–12 March 2018) (7). Chunyun is a period of 40 days—15 days before and 25 days after the Lunar New Year—during which there are high rates of travel within China. To estimate human mobility during the 2020 Chunyun period, which began 10 January, we aligned the 2018 Tencent data based on relative timing to the Spring Festival. For example, we used mobility data from 1 February 2018 to represent human movement on 10 January 2020, as these days were similarly distant from the Lunar New Year. During the 2018 Chunyun, a total of 1.73 billion travel events were captured in the Tencent data; whereas 2.97 billion trips are reported (7). To compensate for underreporting and reconcile these two numbers, a travel multiplicative factor, ?, which is greater than 1, is included (see supplementary materials).

Read more: https://science.sciencemag.org/content/early/2020/03/13/science.abb3221

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Translation: the bulk of infections are from people not exhibiting symptoms...

Link to tweet

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[Bernardo de La Paz]

1. Tweet is exec summary: it's driving this pandemic: "We estimate 86% of all infections were undocumen

[UpInArms]

2. Typhoid marys

Unless we get widespread testing going, we are screwn

[keithbvadu2]

3. Like not checking thousands of people from a ship that probably had the bug?

Like not checking thousands of people from a ship that probably had the bug?

https://www.democraticunderground.com/10142448611

3,800 Leave Cruise Ship Unscreened After Former Passenger Tests Positive

[diva77]

4. and maybe asymptomatic crew will be transshipped and work aboard other cruiseships in the fleet.

[Igel]

6. People are letting politics drive their thinking.

It's human, but it's backwards.

It means from the get-go, most of the infection was driven by people we didn't suspect. It means to contain it we'd have to have run thousands of COVID tests per day, at a minimum--by mid February, millions--mostly on people that were asymptomatic.

*And* that we'd have to know to do this before we had any reason to do this.

Note that this is one line of reasoning, based on distribution and frequency of known cases. It works backwards from where we are to how we got here.

Recently another bit of research worked forwards and comes to the same conclusions. It determined when symptoms and viral shedding first appeared and when reached their maximum and the duration of infectiousness. The people that were *most* infectious reached that point at about day 5 after infection, around 3 days after a test would have resulted in a positive, they stayed that way for days, and they were entirely asymptomatic. In other words, you test somebody today who was exposed yesterday, and you get a negative--but in 4 days they're walking superspreaders that passed your test and show no symptoms. Just wonderful. So you have to test every asymptomatic person every 3-4 days to stop this bug.

Meaning, again, to stop the spread we'd have to test many tens of thousands, if not millions, of asymptomatic people per day. And just because you tested negative on Monday doesn't mean you wouldn't need to be retested on Friday. And you would have needed to start this soon after New Year's 2020. Meaning you'd need to be psychic, have a test before anybody gave you the information for the test, and have at least a thousand labs set up and 10s of millions of test kits. Has the absurdity of this become clear yet?

We need to find scapegoats and blame somebody. We need the universe to be just, we need to find patterns and place blame. Those with religion blame god or the devil of their choice, or displace justice to a future or past life by means of some cosmic accounting making sure your multi-life checkbook keeps a positive balance. Those with politics blame a useful adversary, and if they don't have one, they find one. In this case, it's really unsatisfying to *not* blame Trump because the conclusion keeps coming back: Anybody who did anything reasonable (as opposed to requiring testing especially of people who were asymptomatic just because) would have failed in containment. That's Xi. That's Trump. That's Kim. That's whoever the prime minister du jour of Italy is. The only way to stop it is to treat everybody as though they were superspreaders as soon as the virus is shown to be present, because by the time you know it's there it's already spread. Unless you institute mass testing of the entire population that *could* be affected you'll miss the really nasty sources of infection. And that won't stop it from being introduced again next week, meaning you again get to test the entire population that could be infected. It's a damnable virus that discretely spreads.

Yes, one consequence is that if you're in an area with any COVID present, it means not only that you could have gotten it, but that you spread it. Do you need to think you were a carrier? Not in the least. Those you infected might have just thought they picked up a cold, maybe the flu. But if you were infected and asymptomatic, you were shedding more virus than somebody in the ICU.

Yes, some of the people on that ship probably had it. Then again, they're probably heading to a community where it's already rampant enough that the only thing testing would have done would be to say, "Yup, you have it. Next!" And if the community they were heading to didn't have it, it soon would and the same measures would be required, because *no* country is set up for running a million COVID tests per day. Then again, the only reason for the information is to assuage fear of uncertainty and to be able to point fingers. Otherwise, it's pointless information at this point. Useful for containment, but not mitigation.

[IronLionZion]

5. But if they don't test, then we can all pretend it's not happening

that's the best way to own the libtards and their media manufactured hoax to damage Trump's economy.

Malicious conservatives are deliberately spreading both the virus and blatant misinformation. How can anyone not see that it's spreading way more quickly than other pandemics in recent history?

[RobinA]

7. I Would Be Curious

if they do a study after this is all over as to how many people turn up with antibodies to this thing versus how many people actually got sick.

For example, I had Lyme disease and it was like a nasty flu. Felt like total shit. My father had a classic Lyme bullseye on his arm for WEEKS and never even felt under the weather. Finally got treated, which caused the bullseye to go away, but never, ever had a symptom other than the bullseye. I've read that back in the day, most people had polio and never even knew it. So how prevalent is this Corona going to turn out to be?