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There are various statistics estimating mortality of COVID-19 infections, based on how many diagnosed people have died. These numbers are used by various media to extrapolate how many people will die if the disease spreads uncontrollably.

However, what is missing here are the undiagnosed infected (due to their immune system fighting the virus fast enough and thus only presenting with mild, or no, symptoms).

Do we have any data or estimates for the percentage of infected people that are asymptomatic?

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  • $\begingroup$ I don't find the source right now, so this is only a comment for the moment. But as far as I read, there are not completely asymptomatic patients. They develop symptoms, but these are sometimes misjudged as a normal seasonal flu: Runny nose, headache, sore throat, fever (this not always). $\endgroup$ – Chris♦ Mar 13 '20 at 21:35
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    $\begingroup$ Probably the best way to estimate this is based on molecular/phylogenetic data. I've seen a study go by on Twitter but can't put my hands on it right now (anyone know how to search Twitter for a tweet from the last few days with an image of an iceberg ... ??) $\endgroup$ – Ben Bolker Mar 13 '20 at 22:01
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    $\begingroup$ I'm voting to close this question as off-topic because it is not about biology in the terms of SE Biology but a request for statistics about the current outbreak. $\endgroup$ – David Mar 13 '20 at 23:21
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    $\begingroup$ @David, I continue to disagree with you about appropriate scope ... I'm still planning to answer (if I get around to it before the question gets closed). (The answer actually depends on a lot of interesting molecular evolutionary theory.) $\endgroup$ – Ben Bolker Mar 14 '20 at 0:17
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    $\begingroup$ twitter.com/trvrb/status/1238643293103075329 $\endgroup$ – Ben Bolker Mar 14 '20 at 2:53
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The proportion of individuals infected by SARS-CoV-2 who remain asymptomatic throughout the course of infection has not yet been definitely assessed.

The asymptomatic ratio is thus estimated at 41.6% (95% confidence interval (CI): 16.7%, 66.7%) among evacuees. Because fourteen days have elapsed since their departure from Wuhan—longer than the 95th percentile estimate of the COVID-19 incubation period (Li et al., 2020; Linton et al., 2020)—there is very little probability that the five virus-positive asymptomatic individuals will develop symptoms. Should one of the five becomes symptomatic in the future, the overall asymptomatic ratio would decrease to 33.3% (95% CI: 8.3%, 58.3%).

Our estimated asymptomatic proportion is at 17.9% (95%CrI: 15.5–20.2%), which overlaps with a recently derived estimate of 33.3% (95% confidence interval: 8.3–58.3%) from data of Japanese citizens evacuated from Wuhan [13].

Table S1. Model parameters. All time periods are given in days.

Parameter                     Baseline              Distribution  Reference/reason
                              (alternative values)  
...
Pr(Asymptomatic | Infection)  0.178 (0.1, 0.5)      Beta          Mizumoto et al. (13) (lower, higher)
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