October 14, 2020

expert reaction to preprint modelling likely impact of precautionary breaks (planned, limited duration circuit breaks) on the prevalence of COVID-19

A preprint, an unpublished non peer-reviewed report, has modelled the likely impact of precautionary breaks (planned, limited duration circuit breaks) on the prevalence of COVID-19

This Roundup accompanied an SMC Briefing.

Prof Paul Hunter, Professor in Medicine, UEA, said:

“There is little doubt that an effective circuit breaker lockdown will reduce cases in the short term, depending on how restrictive the lockdown is and how well it is adhered to.  The paper by Keeling and colleagues show this very well as can be seen with the impact of the UK and other lockdowns globally and is currently being seen in Israel.  However, as stated by Keeling these are not long-term solutions.  One of the big issues is that in most countries case numbers increased more rapidly before imposition of control measures than they declined afterwards.  What this means is that after any circuit breaker is imposed there is a gap of about 10 to 14 days before the impact of that is seen in any change in the rate of increase in the infection rates.  After that peak has been reached cases then decline until 10 to 14 days after any relaxation of the lockdown.  The problem is that case numbers generally decline rather more slowly after lockdown than they increased before.  In other words the halving time tends to be longer after a peak than the doubling time before a peak.

“Keeling produced models with various rates of decline after the start of the circuit breaker lockdown.  But, without looking at the actual data on the epidemic a reader may think that the impact of a short circuit breaker would be greater than is likely in the real world.  The model as presented also refers only to new infections and so does not stress the fact that case numbers, hospitalisations and deaths would continue to rise for some time because of the lag in diagnosis, etc.

“So in order to maintain case numbers at a relatively constant rate you would need to have as many as twice as many days in circuit break lockdown as relaxed days making such short lockdowns little different from the more prolonged lockdown we saw in March/April and May.  Such short lockdowns in the UK and as we are seeing in Israel need more than a couple of weeks to achieve a substantial reduction in numbers to the point that the epidemic would be “reset”.  The model presented by Keeling, the recent experience from Israel and our own experience in the UK from spring would suggest that a single short one or two-week circuit breaker lockdown would not have a sustained impact on the trajectory of the current epidemic unless other effective interventions were implemented at the same time and maintained afterwards.”

Prof Liam Smeeth, Professor of Clinical Epidemiology, London School of Hygiene and Tropical Medicine, said:

“This is an important piece of work that demonstrates the value of short periods of increased restrictions – so called circuit-breakers – to reduce transmission and contain spread of the virus.  Crucially, such brief periods can be pre-planned weeks or even months in advance.  This would be likely to help businesses and employees plan and thus reduce the economic impacts.  In addition, it would reduce the need for last minute policy changes that people find so disruptive and confusing.  Introducing a more strategic, longer-term approach to viral control would be positive progress, contrasting with the seemingly ad hoc almost panicked responses we see at present.”

Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“It’s clear that we need to put a break on the outbreak so that we can buy time to allow other interventions, especially those around testing and contact tracing, to work.  It is unlikely that the interventions that have been introduced will have a major effect on case numbers and bring that very important ‘R number’ down.  However, we need to ensure that infection control built around increased testing is fit for purpose, otherwise we will keep flip-flopping between lockdown and relaxation, and this will need us to learn from other places that appear to have been more successful at keeping it under control, whilst minimising social and economic impacts.”

Preprint: ‘Precautionary breaks: planned, limited duration circuit breaks to control the prevalence of COVID-19’ by Matt J. Keeling et al.  This work is not peer-reviewed.

All our previous output on this subject can be seen at this weblink:

www.sciencemediacentre.org/tag/covid-19

Declared interests

Prof Liam Smeeth: “Graham Medley and I both work at LSHTM.”

Prof Jonathan Ball: “No CoIs on this.”