Monday, May 18, 2020

Strategy for a Pandemic: The UK and COVID-19

Sir Lawrence Freedman (member of the Chilcott Inquiry) has written a review of the UK Govt's response to the coronavirus outbreak which can be found here

He explains his motives thusly:

"The inquiry into the United Kingdom’s role in the 2003 Iraq War, of which I was a member, took the view that when inquiring into a contentious area of policymaking, an essential first step was compiling a reliable account. This should be influenced as little as possible by the benefit of hindsight. This article attempts to provide a preliminary account of the development of UK strategy on COVID-19, from the first evidence of trouble in Wuhan in early January to the announcement of the full lockdown on 23 March. As policy-makers claimed to be ‘following the science’, this requires an analysis of the way that the expert community assessed the new coronavirus, the effects of alternative interventions intended to contain its spread and moderate its impact, and how experts’ findings were fed into the policymaking process. It is preliminary because, while there is good material on both the policy inputs and outputs, the material on how the policy was actually made is more speculative."

It's an interesting read, but while reading it I can't help but think of Orwell's aphorism:
"Who controls the past controls the future."
Here is an interesting snippet in which there seems to be a very clear and perhaps important misunderstanding of the time line. Freedman says on p52:

"By that time, the strategy had already begun to shift. Hours after the COBRA meeting, on the evening of 12 March, SAGE met again to hear from Professor Ferguson on the results of his group’s latest modelling. The conclusions, which were made public on 16 March, were startling. What had made the difference was evidence from Italy suggesting that the R0 was more like 3 than 2.5 and, most importantly, that previous estimates of intensive-care requirements had been optimistic."

The paper itself is of course published and uses an R value of 2.4 in the main analysis of mitigation scenarios, with a range of 2.0-2.6 in sensitivity tests. The Oral hearing of the Science and Technology Committee that Freedman cites as the source of his information took place on the Wednesday 25 March 2020 and can be found here. Ferguson is on at 10:15 onwards, with the relevant comments about R0 right at the end of his segment around 10:55. He says rather disingenuously that the new estimate for R0 of around 3 is "within the wide range of values" that had been considered by modelling groups. Certainly not his, and when you take the doubling time into account, it is very much at the edge of Kucharski's work too. 

I think Ferguson is on very dodgy ground indeed in so blithely dismissing this discrepancy in front of the Select Committee as it is critical to the question of how soon and how aggressively we needed to deal with the epidemic. Note that the doubling time (which is what really matters here) depends not only on R0 but also the reproductive time scale of the virus). In fact, as I have documented previously, the SPI-M advice specifically pointed to a 5-7 day doubling time as late as the 18th March at which point they were considering a lockdown for London (only). It was only at the meeting of the 23rd, long after the 12 March date that Freedman refers to, that SAGE learnt of the change of the estimate to 3-5 day doubling, and the lockdown was ordered that same evening. I am no friend of the Tories and there are lots of things they did badly, but specifically in terms of reacting to the abruptly and radically updated scientific advice, their response seems exemplary here.

Also, on p58:
"Given the known sequence for infection, incubation, hospitalisation and death, it is reasonable to conclude that changes in behaviour were having an effect well before 23 March, especially in London."

This may be possible but does not seem necessary. I'm not just drawing on my own modelling here, Flaxman et al consider all the interventions and also find that the lockdown had by far the largest effect on the epidemic with the other earlier interventions being very minor influences in comparison. Their latest estimate shows R0 dropping from 3.9 to about 3.5 during the week prior, then collapsing to about 0.7 on the 23rd, very similar to my own estimate. (as I've discussed before, their sightly larger initial and lower current values for R can probably be attributed to a longer serial interval of 6.5d in their model compared to about 5.5d in mine). Here are both of our latest results, mine as the top plot and theirs in the following two:

Freedman's rosy assessment from p57 onwards of the NHS coping may not be shared by all, particularly the large number of victims who were shut out by the NHS and sent out into the community to die in care homes while infecting many others, with both NHS and care home staff also inadequately protected. If the NHS really had capacity, why did this happen? I know he refers to this subsequently, but doesn't seem to make the connection. "Coping" by refusing treatment to large numbers of sick and dying people isn't really coping, is it?

Anyway, it's an interesting read.


Everett F Sargent said...

It is kind of weird. I 1st downloaded the JCU data on March 24th and the 1st thing I did was doubling time calculations, I don't know if it is because of the relatively small numbers at the start of time of almost any time series, but doubling times are almost always in the 1-3 day range initially. I had those doubling times that very same evening. And I'm very much coming straight out of left field as it were.

I simply don't know, given this ...

Why such a low value for R0 was used initially. Also, my understanding is that lockdowns are a very old strategy.

It has been my personal experience that academics can be slow to come to a decision, they almost always err on the side of caution. The pressure must have been great though at that time, full country lockdown,

Finally, a question. What date did Furgeson, et. al. make their original ~600K UK and ~2.4M US prediction? After all, it was those numbers, afaik that made both the UK/US stand up and pay attention, as best as I can recall.

Everett F Sargent said...

JCU should be JHU.

Phil said...

Cases don't decline very fast at R=0.77

What plan, if any, is there to speed the decline?

Or is the UK just going to open back up on some random day, much as part of the USA has?

I fear I know the results.

PhilScadden said...

Experience here in NZ, using contact tracing data, R0 was around 4. Lockdown dropped it to 0.4 and cases declined quickly after that. I would say you need severe lockdown, everyone in very small bubbles, and efficient testing and contact tracing. I think that horse has bolted in the UK. Having staff moving between different rest homes is also a terrible idea, verging on criminal negligence. Our heroes were the staff that chose as a body, to lockdown in the homes with the ones they cared for.

James Annan said...

Everett, the Ferguson paper was the 16th March though there may have been a draft a little earlier. But there is no mention of R=3 in that, it only goes up to 2.6 as a sensitivity test. Yes it did help to get people to take notice, but still didn't have enough urgency.

Phil said...

Is IFR for the UK and USA greater than 1%?

Not a lot greater mind you.

Remember that the UK and the USA isn't counting every death.

IFR will vary with population age distribution, health care, other health factors...

Layzej said...


Interesting stats. I was surprised to see crude mortality rate estimated at 0.28% to date in NYC, with an expectation that it could reach 1% once this is through.