Ashish K. Jha+ Your Authors @ashishkjha Physician, researcher, and advocate for the notion that an ounce of data is worth a thousand pounds of opinion. Director @harvardgh. Soon, Dean @Brown_SPH Jun. 08, 2020 1 min read + Your Authors

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.

A thread

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

 https://www.medrxiv.org/content/10.1101/2020.05.10.20097543v1.full.pdf 

2/5

So what about the other 80% of people who do have symptoms?

Many of them are shedding virus BEFORE they develop symptoms

 https://www.nature.com/articles/s41591-020-0869-5 

Technically, these folks are PRE-symptomatic, not asymptomatic

But they are asymptomatic at the time they are shedding virus

3/5

Some modeling studies suggest 40-60% of spread is from people when they didn’t have symptoms.

Here are a few refs:

 https://www.acpjournals.org/doi/full/10.7326/M20-3012 

 https://www.medrxiv.org/content/10.1101/2020.04.25.20079103v2 

4/6

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.

5/6

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

6/7

.@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

Fin

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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