What is the ‘R’ value? Why is a rate of number one critical to coronavirus fight? – The Sun

BRITAIN is doing great and scoring an "R value" consistently below one according to the latest coronavirus figures and scientific statistics, which means social distancing is working.

But what is the R value and why does it matter so much?

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What is the R value?

R0, or R nought, refers to the average number of people that one infected person can expect to pass the coronavirus on to.

Scientists use it to predict how far and how fast a disease will spread – and the number can also inform policy decisions about how to contain an outbreak.

For example, if a virus has an R0 of three, it means that every sick person will pass the disease on to three other people if no containment measures are introduced.

It's also worth pointing out that the R0 is a measure of how infectious a disease is, but not how deadly.

Taking London as an example, with a current R value of 0.4 for coronavirus, it means that every for every ten people who have the virus, it will be passed on to only four more people.

The low R value means that if everyone continues lockdown and social distancing measures, London would theoretically be virus free in two weeks.

What does it mean for Covid-19?

The World Health Organisation (WHO) estimated at the start of March that the coronavirus R0 stood somewhere between 2 and 2.5.

The UK is now generally below that because of the lockdown and the social distancing measures we have been doing over the past two months.

In comparison, the seasonal flu is estimated to be roughly 1.3 while measles has a reproductive value of between 12 and 18.

Despite this, these figures are not set in stone because a given pathogen's R value changes with place and time.

Jonathan Ball, professor of molecular virology at the University of Nottingham, told The Telegraph: "R0 is an indication of how much an infectious virus will spread in a population, and various things impact that value.


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"The susceptibility, size and density of the population that the infection is introduced into matters, as well as the infectiousness of the virus itself."

Predictions of the R0 for Covid-19 are currently varied because no one knows exactly how many people have been infected in total.

According to modelling published by Imperial College London, the R value stood somewhere between 3 and 4.6 in Europe before lockdowns came into effect.

What is the R rate in the UK?

The current R rate varies across the UK, but it is consistently below R1 which is the important bit because it means there's no virus spread, but things are generally worse in the North to the point that it the trend could reverse.

New data released May 14 from Cambridge University suggests that in the North East and Yorkshire the R rate – the average number of people an infection person can pass the virus on to – is feared to be at around 0.8.

The South West has an R rate of 0.76, slightly more than the North West which has a rate of 0.73.

Both the East of England and South East have a rate of 0.71, followed by the Midlands with 0.68 and finally London with 0.40.

On May 10, 2020, Boris Johnson urged the British public to help reduce the R value.

In his address to the nation, he said: "It depends on all of us – the entire country – to follow the advice, to observe social distancing, and to keep that R down."

He added: "We must make sure that any measures we take do not force the reproduction rate of the disease – the R – back up over one, so that we have the kind of exponential growth we were facing a few weeks ago.

During one of the Downing Street press conferences, Sir Patrick revealed that it was "highly likely" there is an R value in the community of less than one.

This means that every infected individual passes the disease to less than one other person.

This shows the lockdown has had a positive impact on the coronavirus outbreak as to bring an outbreak under control the R0 value needs to fall below one.

However, when the number remains higher than one, the epidemic will grow.

Sir Patrick admitted that the R0 value could be higher in some care homes and hospitals.

He said: "As I’ve said, it’s not true that the R is necessarily below one in every hospital or in every care home, and that’s the important area that we now need to look at and make sure that the appropriate measures are in place to try and reduce the R there.

"But it doesn’t change the overall view that I’ve described, that the R overall is below one and therefore we expect to see the slowing and the turn of the epidemic."

What can reduce the R rate?

There are lots of infection control measures experts can use to push this number down and reduce the spread.

A study in the Lancet in April, for example, estimated that travel restrictions in Wuhan caused R0 to drop from 2.35 to 1.05 after just one week.

Sir Patrick said that the draconian social distancing measures introduced in the UK have had a substantial impact so far.

This is because as less people come into contact with one another, there is less chance for the virus to spread.

He said on Thursday, April 16: "The social distancing measures are needed to reduce the levels right down to a low level.

"At that point there may be decisions about which ones to relax and which ones not to relax.

"It’s important to keep the R below one, and this is all about trying to reduce contacts, particularly between households, reduce transmission and keep the levels low across the community."


And Sir Patrick added that even small changes in the measures that are in place "could lead to the R going above one."

According to a pre-print study from the London School of Hygiene and Tropical Medicine, the average number of people an individual comes into contact with each day has dropped by 73 per cent since the UK’s lockdown began.

“This would be sufficient to reduce R0 from a value from 2.6 before the lockdown to 0.62 during the lockdown, indicating that physical distancing interventions are effective,” the study, which tracked over 1,300 adults and has not yet been peer reviewed, concluded.

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