This new study is troubling. It indicates that the majority of new cases are tied SILENT transmission from a combination of the presymptomatic stage and asymptomatic infections. Ie. NOT from people showing overt symptoms!
What does this mean? Thread 🧵. #covid19
What does this mean? Thread 🧵. #covid19
2) It means that even if all symptomatic cases are isolated, a vast outbreak can still unfold.
Furthermore, they found that that over 1/3rd of silent infections must be isolated to suppress a future outbreak below 1% of the population.
Furthermore, they found that that over 1/3rd of silent infections must be isolated to suppress a future outbreak below 1% of the population.
3) “symptom-based isolation must be supplemented by rapid contact tracing and testing that identifies asymptomatic and presymptomatic cases, in order to safely lift current restrictions.”
➡️ Thus, they suggest we need to test beyond people with symptoms, and trace them fast!
➡️ Thus, they suggest we need to test beyond people with symptoms, and trace them fast!
4) “Given inadequacy of symptom-based isolation to control COVID-19 outbreaks... Combined with case isolation, our results indicate that 33% and 42% detection and isolation of silent infections would be needed to suppress the attack rate below 1%”
5) The conclusion that “silent transmission alone can sustain outbreaks even if all symptomatic cases are immediately isolated” has also been seen before: contact tracing show substantial role of presymptomatic transmission among COVID-19 cases in Singapore & 468 cases in China.
6) Further they think their finding is an underestimate. “our estimation for isolation of silently infected individuals is a lower bound, as inevitable imperfections in isolation of symptomatic cases translates to need to prevent silent transmission.” pnas.org/content/early/…
7) All in all, it’s looking like this pandemic will continue to burn until we have extremely rigorous and fast contact tracing, and that we start to test and find asymptomatic & pre-symptomatic people. Doing the latter will need a new ramp of mass testing that we don’t have yet.
8) that said we should do it willy nilly for any random person. mass testing should still be targeted to high transmission risk groups like college dorm and fraternity students. Hence pooled testing or groups of such people might be efficient. But all in all, we need to ramp up.
9) People do wonder how did some countries seem to eliminate it - I think the answer is THEY MOVED FAST AND EARLY. By moving early, numbers become much better than a high prevalence. (1% attack of 10 people is negligible, while 1% of 100,000 still yields a large non-zero value).
