IC COV19 modelling group: suppression vs mitigation

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Eddy Edson

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Published today: https://www.imperial.ac.uk/media/im...-College-COVID19-NPI-modelling-16-03-2020.pdf

I think this is one of the main groups informing the UK govt & this work no doubt has contributed to the recent policy shifts.

Two fundamental strategies are possible: (a) mitigation, which focuses on slowing but not necessarily stopping epidemic spread – reducing peak healthcare demand while protecting those most at risk of severe disease from infection, and (b) suppression, which aims to reverse epidemic growth, reducing case numbers to low levels and maintaining that situation indefinitely.

Each policy has major challenges.

We find that that optimal mitigation policies (combining home isolation of suspect cases, home quarantine of those living in the same household as suspect cases, and social distancing of the elderly and others at most risk of severe disease) might reduce peak healthcare demand by 2/3 and deaths by half. However, the resulting mitigated epidemic would still likely result in hundreds of thousands of deaths and health systems (most notably intensive care units) being overwhelmed many times over.

For countries able to achieve it, this leaves suppression as the preferred policy option. We show that in the UK and US context, suppression will minimally require a combination of social distancing of the entire population, home isolation of cases and household quarantine of their family members. This may need to be supplemented by school and university closures, though it should be recognised that such closures may have negative impacts on health systems due to increased absenteeism.

The major challenge of suppression is that this type of intensive intervention package – or something equivalently effective at reducing transmission – will need to be maintained until a vaccine becomes available (potentially 18 months or more) – given that we predict that transmission will quickly rebound if interventions are relaxed.

We show that intermittent social distancing – triggered by trends in disease surveillance – may allow interventions to be relaxed temporarily in relative short time windows, but measures will need to be reintroduced if or when case numbers rebound. Last, while experience in China and now South Korea show that suppression is possible in the short term, it remains to be seen whether it is possible long-term, and whether the social and economic costs of the interventions adopted thus far can be reduced.
 
Because this is the Internet I'm allowed to express opinions despite having zero qualifications ...

Suppress. Get your resources together. Put in place surveillance, testing, isolation and care resources. Unsuppress. Quickly detect, trace & isolate new outbreaks while the rest of the country goes about its business.

Clue: None of South Korea, Taiwan, Singapore, HK have come to a long term halt. This is because they have put in place that strategy, and they can do that because this thing doesn't transmit like the flu: you generally need close contact for some extended period, and chains are relatively easy to break.
 
In yesterdays press conference, Chris Witty said that a "bedside test" for coronavirus infection and a test for antibodies to show whether somebody has been infected are both very close. The enthusiasm with which he said it implied that he thinks both will be game changers when it comes to understanding what has been going on and predicting the outcome.

Hancock was a bit more waffly in questions on his statement in parliament on the subject. I'm wondering whether a decision was made not to expand testing using current methods on the assumption that these new tests would be successfully developed in the short term and nobody wants to say so.
 
Apparently this work was also the main reason for the dramatic Trump-shift yesterday.

I'm sure these people are all good with computers but it's really not very comforting that the highest level medical decisions are being driven by modelling which seems to be based on a whole bunch of untested assumptions, apparently favouring eg gloom from Italy over light from Asia.
 
I got the impression from WHO yesterday, that they have lots equipment to perfom tests and are willing to supply countries with.
 
An Ars Technica explainer for the model: https://arstechnica.com/science/202...-of-different-methods-of-coronavirus-control/

FWIW, IMO I think it's pretty clear in model terms that the most powerful lever is reducing R0 and that the best way of doing that is by surveillance, tracing and isolating pretty much all contacts. As recommended by the WHO and implemented in the Asian countries which so far are succeeding in keeping the beast leashed.

The only rationale for "suppression" is that you didn't have a good surveillance system in place and you let the thing get out of control and the contact tracing job is now too difficult - despite the lead time and the longer-term warnings extending over years from SARS, MERS etc.

Suppression gives you time to correct your deficiencies and be ready to unsuppress, let your country start again and do the right things. As in China and South Korea.
 
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Just rabbiting on more about this ...

Delving into the nerdy details you can infer that under their best case scenario - suppress everything early - the infection rate is a bit under 1%.

That's a lot better than the ~80% they come up with for the uncontrolled situation but I really question whether it accurately reflects anything like a best case scenario.

In China, the infection rate is something less than 0.01%. In South Korea it's less than 0.02%. Both places growth has been reduced to almost nothing, at least for the moment. In most parts of both countries, it's nothing like total "suppression".

In Italy it's current about 0.05% and obviously growing quickly for the moment. But the lock-down lag takes a couple of weeks to kick in, and in the first province to be locked down, growth has topped out and the numbers will soon show the same thing for the rest of the country.

Maybe the rate in Italy goes a lot higher than 0.05% but what reason, taking into account reality and not just modelling assumptions, for assuming something as high as 1%?

Assuming a best-case peak < 0.1% infection rate for the UK, instead of around 1% , obviously presents a very different picture in terms of ICU bed requirements - there would be plenty - etc.

Of course we're probably now in the situation where some suppression is necessary to achieve that kind of outcome. But the whiff of hysteria on high and undue deference to the nerds isn't very impressive.

It'd be much more useful to do this:

 
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This is being flagged around by virologists and epidemiologists on Twitter: https://threader.app/thread/1240444821593944064

A Seattle-based scientist's reflections on the IC model. Nope; what you want to do is leverage technology for wide-spread testing and tracking, breaking chains and stopping the thing in its tracks. Also deploy serological testing to work out who's immune and get them out of isolation ASAP.

An "Apollo program". (Though apart from the serological testing, it's just what's recommended by WHO and implemented in the Asian countries which know what they're doing. Not *that* big a deal to get together if govt's and their health advisors have a clue.)

The serological testing bit doesn't exist yet for full-scale roll-out but several high-profile labs are almost there or have it developed and under test.

A 1% "best case" infection rate target looks foolish and unwarranted to an increasing number of people who should know what they're talking about.
 
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