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"New evidence has emerged from China indicating that the large majority of coronavirus infections do not result in symptoms." (cue internal screaming)
The BMJ should know that asymptomatic and presymptomatic are. NOT. THE. SAME. THING!!!!! https://www.bmj.com/content/369/bmj.m1375
The BMJ should know that asymptomatic and presymptomatic are. NOT. THE. SAME. THING!!!!! https://www.bmj.com/content/369/bmj.m1375
Asymptomatic transmission is from patients that *never* develop symptoms.
Presymptomatic transmission is from patients that haven't developed symptoms *yet*.
Presymptomatic transmission is from patients that haven't developed symptoms *yet*.
This reports on a study from China that observed that 78% of patients testing positive for #SARSCoV2 #HCoV19 #COVID19 #coronavirus did not have symptoms. Scary, right? It suggests that the majority of infected patients are silently transmitting virus...BUT (and this is a big BUT)
This study ONLY looked at a 24 hour period and from what I can tell didn't follow up on the patients tested. So while the patients were asymptomatic THAT DAY, it's unknown how many of them developed symptoms later on.
Furthermore, this was a study of 166 positive patients total from one day. As of today, there are 82,718 confirmed cases in China. That's sampling 0.2% of confirmed cases, so to extrapolate that to "the large majority" of COVID cases is...a stretch.
https://gisanddata.maps.arcgis.com/apps/opsdashboard/index.html#/bda7594740fd40299423467b48e9ecf6
https://gisanddata.maps.arcgis.com/apps/opsdashboard/index.html#/bda7594740fd40299423467b48e9ecf6
Later in the piece: "Citing classified data, the @SCMPNews said that China had already found more than 43,000 cases of asymptomatic infection through contact tracing." Again, no word on whether those "asymptomatic" cases eventually became symptomatic.
Data shows that presymptomatic transmission clearly happens, and probably happens frequently. There is definitely a substantial risk that people who don't know they are sick can spread virus to others. This is why physical/social distancing is critical absent widespread testing.
Which is why it was disturbing to read this opinion from two prominent scientists at the end of the article: "Lockdown is going to bankrupt all of us and our descendants and is unlikely at this point to slow or halt viral circulation as the genie is out of the bottle."
THAT IS NOT TRUE. Yes, the genie is out of the bottle. Yes, people can transmit without knowing they are sick. But saying that because 80% of patients are definitely "asymptomatic" based on this evidence and thus we should just end lockdown & accept our fate is dangerously wrong.
For one thing, we don't know how many of those 80% will develop symptoms, and of those, how many will develop severe COVID-19 requiring hospitalization or ICU care/ventilation, etc. It would be a grave mistake to assume that 80% of patients will require no medical care at all.
WHO reports that truly asymptomatic cases are rare. We should address presymptomatic transmission by testing and isolation. We should NOT say "no more lockdowns because most people are always asymptomatic from beginning to end so let's just accept our fate" 
It's disappointing to see a major medical journal like BMJ publish such a sweeping statement based on such scant evidence (also, I couldn't find a link to the actual data besides a statement from the Chinese National Health Commission).
Bottom line: these reported data don't make the crucial distinction between asymptomatic and presymptomatic. These are different and must be addressed as such. Don't assume that the vast majority of coronaviruses cases are asymptomatic throughout the course of infection.
