R value: What is the R value? What does R mean?

Dominic Raab has confirmed the UK will continue to be on lockdown for a further three weeks during the coronavirus pandemic. The Foreign Secretary said the lockdown has been successful in slowing the spread of infection, and this is all down to reducing something called the R value, otherwise known as a reproductive value.

What is R value?

R0, or R naught, refers to the average number of people that one sick person goes on to infect in a group that has no immunity.

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.

The R value is therefore a measure of how transmissible, or contagious, a disease is.


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According to the World Health Organisation, the R0 of coronavirus so far falls between 2 to 2.5.

A given pathogen’s R value changes with place and time.

An R value of one means the average person who gets that disease will transmit it to one other person; in that case, the disease is spreading at a stable rate.

An R of more than one means the disease spreads exponentially.

For coronavirus to be considered dying out, that means its R0 must fall to below one.

Controlling social interactions among populations is absolutely essential to bringing the R0 down to less than one, and would also spell the end of the official pandemic.

The likelihood that an infected person gets someone else sick depends on many factors, which can be tough to estimate and vary based on circumstances.

Those can include: the way the virus gets transmitted (through the air or in bodily fluids); whether a virus is contagious during its incubation period; how long that incubation period lasts; and how many people the average patient has contact with.

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However, this can vary considerably from patient to patient.

A person who gets sick might stay inside for the next week, or they might continue life as normal: going to work, the shops, socialising with friends and going on holidays.

The UK’s Chief Scientific Adviser Sir Patrick Vallance said in tonight’s press conference that once the R0 is absolutely certain to be below one, the country could consider which lockdown measures to ease.

He said: “Sage looked very carefully at all of the evidence and is of the opinion that it is highly likely that the R is below one – the transmission force of the virus is below one, meaning that one person will, on average, be infecting fewer than one other person.

“That’s an important change. It means in the community it’s likely that the virus and the epidemic is now shrinking.”

Asked whether the elderly would be the last to be released from the measures, he said: “The aim there is to try and do that in a way that allows everything to start moving more towards normal – not to segregate on certain groups and say there is a differential approach towards this.

“It may be necessary when you look at different jobs and different things to think about how you do that in a way that is safe, but the aim, certainly in terms of how we are doing this from a scientific angle, is to understand the basic principles that reduce transmission and allow the policy makers to take those basic principles and apply them in a number of different settings.”

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