Originally Posted by
germanaviator
Here is an excellent, recent article on asymptomatic spread from the British Medical Journal
https://www.bmj.com/content/371/bmj.m4851
In short, asymptomatic spread is much less of a thing than initially estimated. Based on whar they know now they thini asymptomatic spread accounts for less than 20% of the cases.
However, many people who were initially thought to be asymptomatic went on to develop symptoms later, so were really pre-symptomatic.
Pre-symptomatic people play a significant role in transmission as they carry enough life virus to be contagious without having symptoms yet.
The article also talks about the limitations of PCR testing as the sole criterion for determining infection.
Great article. I wish our policy decisions were based on this kind of scientific review rather than hysteria. I do take exception to the one thing that you bolded though - I don't remember seeing any conclusion in that article that presymptomatic people play any significant role - in fact, I think the point was we don't know and are making assumptions (perhaps invalid) based on testing not for infectiousness but just for genetic presence of virus, past or present.
From the article - "
It’s also unclear to what extent people with no symptoms transmit SARS-CoV-2. The only test for live virus is viral culture. PCR and lateral flow tests do not distinguish live virus. No test of infection or infectiousness is currently available for routine use. As things stand, a person who tests positive with any kind of test may or may not have an active infection with live virus, and may or may not be infectious"
Also "The transmission rates to contacts within a specific group (secondary attack rate) may be 3-25 times lower for people who are asymptomatic than for those with symptoms. A city-wide prevalence study of almost 10 million people in Wuhan found no evidence of asymptomatic transmission. Coughing, which is a prominent symptom of covid-19, may result in far more viral particles being shed than talking and breathing, so people with symptomatic infections are more contagious, irrespective of close contact. On the other hand, asymptomatic and presymptomatic people may have more contacts than symptomatic people (who are isolating), underlining the importance of hand washing and social distancing measures for everyone."
This makes too much logical sense, though. Instead we figure we should triple mask up.