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Estimated coronavirus reproduction rate appears to increase

UK News | Published:

Experts say the so-called R value is now between 0.7 and 1.0.

A woman wearing a face mask walks past Piccadilly Circus Underground station

The latest estimate is that the range for the reproduction rate of coronavirus – the R value – has increased slightly across the UK, the Government Office for Science has said.

R measures how many people on average one infected person transmits the disease to.

Last week the R in the UK was thought to be between 0.5 and 0.9 but the estimate is that it is now between 0.7 and 1.0.

The rise is thought to be driven by the virus spreading in care homes, and the data does not take into account the easing of lockdown measures.

Officials have said the easing of lockdown measures depends on the R value staying below one.

The Scientific Pandemic Influenza Group on Modelling (SPI-M), a sub-group of the Scientific Advisory Group for Emergencies (Sage), has built a consensus on the value of R based on expert scientific advice from multiple academic groups.

The range of 0.7 to 1.0 is based on the latest data available to determine infection and transmission rates.

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As data on infection is estimated through data on symptomatic cases, hospitalisations or deaths, there is a delay of around two to three weeks because there is a lag between people becoming infected, entering hospital, and dying.

The range announced on Friday applies to data before the adjustments to lockdown restrictions that came into place earlier this week in England.

Therefore there is no real-time figure for R, as it reflects the situation around three weeks prior.

HEALTH Coronavirus
(PA Graphics)

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Sage is confident that overall the R is not above one, meaning the number of infections is not increasing, and is very likely to be decreasing.

Experts say R is not the only important measure of the epidemic, as it indicates whether the epidemic is getting bigger or smaller but not how large it is.

They say it should always be considered alongside the number of people currently infected.

If R equals 1 with 100,000 people currently infected, it is a very different situation to R equals 1 with 1,000 people currently infected.

Sir Patrick Vallance, the Government’s chief scientific adviser, said: “R is one of the important things you can track to understand an epidemic.

“If you can estimate R, then you have part of a reliable tool for planning how to combat the virus.

“If the R is higher than one that means this disease is growing exponentially and will keep on spreading to more and more people.

“To keep R below one and control the virus, it is vital that people stay alert and continue to follow the latest Government guidelines to the letter.

“In the coming weeks we will update this estimate regularly.”

R is an average value that can vary in different parts of the country, communities, and sub-sections of the population.

It cannot be measured directly so there is always some uncertainty around its exact value.

Deputy chief medical officer Dr Jenny Harries told the daily Downing Street press conference: “R is a very standard way of looking and comparing what is happening, and it is a really important measure.

“But the real outcome that we are looking for is a reduction in the number of cases and getting rid of the epidemic in the UK.

“So that is our focus, not R. R is a representation of what is happening in that fight.”

Health Secretary Matt Hancock said: “We are constantly keeping the R under review. We don’t think that it is above one. So that meets that test.

“It is an incredibly important figure for policymakers but it is one data point to look at alongside the level of new cases.”

Reacting to the latest estimates of R, Professor Rowland Kao, Sir Timothy O’Shea professor of veterinary epidemiology and data science, University of Edinburgh, said fluctuations in the value are to be expected.

He explained: “It could for example experience a temporary rise because of the introduction of a random case into a new area but then decline again as the R in that particular location starts to decline.

“These fluctuations will likely become more pronounced as numbers go down, and so it is important to emphasise the overall trend, rather than a single point estimate.”

He added: “Increases in R matter much more if the prevalence is high, as the overall number of new cases is a critical factor in determining, for example, additional burden on ICUs and logistical requirements.”

Professor Keith Neal, emeritus professor in the epidemiology of infectious diseases, University of Nottingham, said that if R is being pushed up by care homes, it is not an issue for community transmission.

“Care homes need to be controlled by infection control, the R in care homes does not influence your control measures in these circumstances,” he said.

“The community R is what is crucial for determining what social distancing measures are needed to control transmission.”

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