Yesterday's confusing announcement from WHO was treated as breaking news, supposedly an upending of our understanding of the risk of transmission from non-symptomatic people. However (as their attempts to clarify today indicate), our understanding has not really changed.
There is a significant amount of evidence that non-symptomatic (pre-symptomatic & true asymptomatic) transmission occurs, and can in fact be an important contributor to transmission.
wwwnc.cdc.gov/eid/article/26…
wwwnc.cdc.gov/eid/article/26…
I don't know why WHO chose this moment to make an announcement about true asymptomatic transmission being a low risk, but my read is they are saying there is little evidence to show that transmission from true asymptomatic cases to others happens regularly.
This absence of evidence may be because it's hard to actually identify this phenomenon even with careful study, or it may indicate that in fact, true asymptomatics are only rarely the source of infection for others. WHO seemed to be leaning toward the latter in its announcement.
But, this doesn't necessarily apply to pre-symptomatic/ mildly symptomatic cases. The true risk of infection from non-symptomatic cases is unknown, but it's not zero and it may in fact be quite high (some estimates run from the maybe 16%- over 50% of transmission from such cases.
A helpful thread here
I should add that WHO experts didn't even make an "announcement", it was information provided in response to a reporter's question yesterday. I should have said "statement" rather than "announcement" in the tweets above.
And always good advice to be kind.
Another helpful thread from @nataliexdean giving us the bottom line.
A good write-up on earlier statements and WHO's clarifications.
statnews.com/2020/06/09/who…
statnews.com/2020/06/09/who…
