Thread by @mvankerkhove

1/ Re-sharing this thorough systematic review & meta-analysis of % asymptomatic infection & asymptomatic /presymptomatic/ symptomatic transmission of #SARSCOV2 - @nicolamlow & co

journals.plos.org/plosmedicine/a…

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 👇

3/ Review addressed 3 questions:

1️⃣what proportion of cases never experience symptoms at all during their infection?

Findings: Estimate 20% (95%CI 17–25)

4/
2️⃣ 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/ 3️⃣What % 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 0.10–1.27) & 🔽 for presymptomatic compared to symptomatic cases (0.63 95% CI 0.18–2.26)

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!

7/ Implications for gov’ts: 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.

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

9/ Thorough contact tracing will eventually start to “catch up” 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.

10/ I’ve heard so many times that it’s too difficult to do contact tracing because “most cases are asymptomatic“.

However available data doesn’t 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.

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.

Last/

I shouldn’t 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.

Let’s work together to end this pandemic.