Wobblers
Euthermic
- Location
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I was quoting the BBC, but I don't know their source.
That said, I've also read a number or reports like the WHO's that put the percentage of symptomless infections much higher.
I suppose one reason for the difference could be how you define a symptom, for example whether you include something like loss of sense of smell, which is reportedly very common, or just count the classic fever/headache/breathing symptoms.
It's a big issue. We still don't know with any certaincy about how this virus affects people - or, just as importantly, why the consequences for some are so much so severe than others. The papers I've looked at and posted links to a few weeks ago (seems a lot longer now!) had data which suggested that at least 90% of infections were going unnoticed by the authorities. The lowest figure, 67%, was used by Neil Ferguson in modelling the consequences of the epidemic in his paper that changed government policy back in March. This means that only the most severe infections are noted, and that most are mild or asymptomatic. Which is a good thing - it means the actual case fatality rate is lower than the published figures.
What is relevant here is that these people with mild symptoms are still infectious. We need to get those people into quarantine. We can't test everyone, but testing those with the obvious symptoms -and isolating them! - is an essential first step. This is where contact tracing comes in - to test those that have been in contact with the overtly infected and isolate those which test positive. Note that there is no country which has succeeded in stemming this virus by use of an app alone. In every case it's been through the use of testing, contact tracing and quarantine.
An app that misses 90% of all potential transmissions is of little use. The case of Singapore amply demonstrates this. They did well in the beginning, containing the virus using testing and contact tracing. Unfortunately, CV19 cases have risen sharply - seemingly at the same time that they failed to adequately test their migrant worker communities. The Singapore contact tracing app has had little effect in slowing the spread of the virus.