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1/ Re-sharing this thorough systematic review & meta-analysis of % asymptomatic infection & asymptomatic /presymptomatic/ symptomatic transmission of #SARSCOV2 - @nicolamlow & co https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1003346
2/ (Preprint of this has been available for some time, & peer-review paper available in Sept) but re-sharing to make a few points still critical today.
We have a long way to go, but we can #ControlCOVID
hear me out
We have a long way to go, but we can #ControlCOVID
hear me out
3/ Review addressed 3 questions:
what proportion of cases never experience symptoms at all during their infection?
Findings: Estimate 20% (95%CI 17â25)
what proportion of cases never experience symptoms at all during their infection?Findings: Estimate 20% (95%CI 17â25)
4/
what % of people who are asymptomatic when diagnosed develop symptoms later?
Findings: 31% (95% CI 26-37) from published studies following patients through course of infection. However, since all cases start asymptomatic, authors est 80% (95% CI 75-83) develop symptoms
what % of people who are asymptomatic when diagnosed develop symptoms later? Findings: 31% (95% CI 26-37) from published studies following patients through course of infection. However, since all cases start asymptomatic, authors est 80% (95% CI 75-83) develop symptoms
5/ 
What % of #SARSCOV2 transmission is by people who are either asymptomatic or presymptomatic?
Findings: The SAR was
in contacts of asymptomatic than symptomatic cases (RR 0.35, 95% CI 0.10â1.27) & for presymptomatic compared to symptomatic cases (0.63 95% CI 0.18â2.26)
What % of #SARSCOV2 transmission is by people who are either asymptomatic or presymptomatic?Findings: The SAR was
in contacts of asymptomatic than symptomatic cases (RR 0.35, 95% CI 0.10â1.27) & for presymptomatic compared to symptomatic cases (0.63 95% CI 0.18â2.26)
6/ Modelling studies fit to data found a higher proportion of all #SARSCoV2 infections resulting from transmission from presymptomatic than asymptomatic cases
Also remember that an estimated 10-20% of cases are responsible for ~80% of transmission events @hkumed =clusters impt!
Also remember that an estimated 10-20% of cases are responsible for ~80% of transmission events @hkumed =clusters impt!
7/ Implications for govâts: Active case finding, quick test results & contact tracing is critical to 
transmission. @WHO has advised this since the beginning and many countries have successfully #ControlledCOVID
Early clinical care & supported quarantine are absolutely key.
transmission. @WHO has advised this since the beginning and many countries have successfully #ControlledCOVID Early clinical care & supported quarantine are absolutely key.
8/ 
Impt for areas that are overwhelmed &/or transmission is intense:
If you can start with symptomatic cases & cluster investigations, isolating and caring for these cases;
& robustly find & support quarantine of close contacts, you will start to break chains of transmission
Impt for areas that are overwhelmed &/or transmission is intense:If you can start with symptomatic cases & cluster investigations, isolating and caring for these cases;
& robustly find & support quarantine of close contacts, you will start to break chains of transmission
9/ Thorough contact tracing will eventually start to âcatch upâ with finding more mild & asymptomatic subsequent cases, who will ALREADY be separated from others because they are in quarantine when identified
Contact tracing for those cases continues... and on & on.
Contact tracing for those cases continues... and on & on.
10/ Iâve heard so many times that itâs too difficult to do contact tracing because âmost cases are asymptomaticâ.
However available data doesnât support this assumption.
We need to be strategic and smart with our resources.
However available data doesnât support this assumption.
We need to be strategic and smart with our resources.
11/ Asymptomatic & presymptomatic transmission certainly makes control harder, but not impossible.
@WHO has warned of this provided guidance on this since Feb.
Papers like this provide robust analyses & help quantity risks.
@WHO has warned of this provided guidance on this since Feb.
Papers like this provide robust analyses & help quantity risks.
12/ So what does this mean for you:
Reduce your chances of infection:
Stay distant from others
Avoid crowded places
Clean 
Open a window
Stay home if unwell; isolate if case; quarantine if contact
#DoItAll
Your actions can help end this pandemic.
Reduce your chances of infection:
Stay distant from othersAvoid crowded places Clean Open a windowStay home if unwell; isolate if case; quarantine if contact
#DoItAll
Your actions can help end this pandemic.
Last/
I shouldnât need to add, but this has profoundly bothered me for many months because of the confusion caused:
@WHO has NEVER said that asymptomatic cases do not transmit.
Never.
Letâs work together to end this pandemic.
I shouldnât need to add, but this has profoundly bothered me for many months because of the confusion caused:
@WHO has NEVER said that asymptomatic cases do not transmit.
Never.
Letâs work together to end this pandemic.
