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expert reaction to latest R number published by government, the range being 0.7-1

The government have announced that the R number for COVID-19 in the UK is now between 0.7 and 1. 


Dr Konstantin Blyuss, Reader in Mathematics at the University of Sussex, said:

“Since R number gives an approximation of how the number of cases is growing, on any day it is being updated using the data from some time ago.

“Due to a lag in reporting the cases and the natural delay in the onset of symptoms plus a potentially large number of asymptomatic carriers, it is really challenging to get good estimates for this quantity.

“In this respect, the R number today shows only part of the picture of how the epidemic situation is changing, but it is, perhaps, too early to say how much of the effect the easing of lockdown over the last week has had on this number.”

Dr Yuliya Kyrychko, Reader in Mathematics at the University of Sussex, said:

“With estimates of R having such a wide margin, and given the uncertainty in reporting of data, one cannot really say in a conclusive manner whether the epidemic situation has genuinely changed.

“This number will, obviously, be different for different regions and different settings, which adds further uncertainty to providing some top-level aggregate values of R.

“Given the complexity of calculating R, relying solely on it to determine when to lift the country-wide lockdown could be misleading.

“Perhaps, in addition to R, having some easily verifiable conditions (such as X number of new cases per 100,000 in a given period of time) would allow a better, more adaptive and straightforward approach to lifting the lockdown.”


Prof Keith Neal, Emeritus Professor in the Epidemiology of Infectious Diseases, University of Nottingham, said:

Because of how R is calculated, what can this tell us, if anything, about the situation today?

“The figure for R will include all possible available data sources to obtain an as accurate figure as possible.

Does it tell us about R number in different settings e.g. community vs. care homes and hospitals? Is this important to know?

“R is only really appropriate for community cases.  Transmission in hospitals and care homes is controlled by infection control, not social distancing measures. Community restrictions will have little if any impact on spread within care facilities.

Is this telling us about R after restrictions have been lifted slightly in England? Or is it too early to see the impact of this?

“It is past one average incubation cycle so the lifting of restrictions has clearly not had a major impact on transmission which would be reflected in the R value.

Is it surprising that it’s not changed or is that expected?

“Not particularly surprising as outside activities pose very little if any risk of infection coupled with social distancing.

Does this have any implications for the roadmap of lifting restrictions?

“We are still over a week away from June 1st so worth waiting for another week before making a decision.

What else apart from R must be considered?

“The number of people who are currently infectious is also important as the number of new infections is this number multiplied by R.

Any other comments?

“As past infection rises, as seen in London, the effective R falls as there are less people who could get infected.  Another factor is that R will vary across the country and we need to understand more about the reasons for this as the differences could be replicated in areas with higher rates of infection.”


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