Estimated coronavirus reproduction rate appears to increase

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.

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.

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.

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