This from @WHO is getting a lot of attention and creating confusion.
I want to quickly share what I understand about this.
Bottom line question:
Are infected people without symptoms an important cause of spread?
My best guess: yes.
First, about 20% of people who are infected likely never develop any symptoms.
They are truly asymptomatic.
Some variation in estimates on this. Lots of data points but here's a preprint
So what about the other 80% of people who do have symptoms?
Many of them are shedding virus BEFORE they develop symptoms
Technically, these folks are PRE-symptomatic, not asymptomatic
But they are asymptomatic at the time they are shedding virus
Some modeling studies suggest 40-60% of spread is from people when they didn’t have symptoms.
Here are a few refs:
So – it might be @WHO is drawing a distinction between asymptomatic spread and pre-symptomatic spread.
And it may be there isn't a lot of asymptomatic spread but plenty of pre-symptomatic spread.
Would be helpful to get the full report that they are referencing.
Both asymptomatic AND pre-symptomatic spread huge problem for controlling disease
Because folks shedding virus while asymptomatic
Pre-symptomatic has one advantage: you can use contact tracing to find folks they infected
But that doesn’t help prevent presymptomatic spread
.@WHO communication here not stellar
If folks without symptoms truly "very rarely" spread virus, would be huge.
But such a statement by @WHO should be accompanied by data.
Asymptomatic spread is Achille's heal of this outbreak
Would love to be wrong. Need to see data
More on @WHO comment by @mvankerkhove
As I read her follow-on tweets, best guess is she really is differentiating asymptomatic vs pre-symptomatic
Two key points:
1. People without symptoms definitely spread disease (so wear a mask)
2. @WHO should be clearer in communication
You can follow @ashishkjha.
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