Despite the UK lockdown loosening, covid-19 is still a huge challenge. Over 40,000 people have died from covid-19 in the UK. There is continuous research going into managing the pandemic. It can be difficult to understand the different models used to monitor the crisis. In this article, we break down everything to do with the R number and why it is important.


r number


What is the R number?


The R number stands for Reproduction number. R is a measure of the average number of people one person with coronavirus will go on to infect. If R is above 1, an outbreak has the potential to grow exponentially.

It is thought that the UK initial R number, prior to lock-down measures, was approaching 4. This means that at that time – the virus was spreading out of control.


If the number is lower than 1, the disease should eventually peter out, as an insufficient number of new people with symptoms to sustain the outbreak.


As an example; if 100 people were covid19 positive when the R stands at 0.5, scientists estimate that they will have passed it on to just 50 people. If the rate remains at 0.5, those 50 people would potentially pass it on to another 25 people before they are no longer infectious.

This then reduces to just 13 people as those 25 patients recover from the virus, they infect just a further 7, then 4, then 2 and finally to one. The virus then hopefully dies out.


However, different parts of the UK and the World have higher and lower R numbers. Because we are usually such a mobile population, travelling and mixing with one another on a face to face basis, trying to control the virus in the long term will remain a challenge.


This is a new virus, with no cure and no vaccine. It is likely to be with us for a while and we will need to learn to live with this ‘new normal’ to remain alert and ensure we are not unwittingly fuelling its resurgence and spread.


A comparison with other diseases:


Measles has one of the highest numbers with a reproduction number of 15 in populations without immunity. It can cause explosive outbreaks.


A further problem with Covid-19 is that people can spread the virus without having any obvious symptoms themselves. This makes it far more difficult to contain. Compared with a deadly disease like Ebola, where you are not contagious until you have developed symptoms.


How is the R number calculated?


It is not possible to capture the moment people contract the virus; so instead scientists work backwards.

Using data – such as the number of people dying, admitted to hospital or testing positive for the virus – allows you to estimate how easily the virus is spreading.

Generally, this gives a picture of what the R number was two to three weeks ago. Regular testing of households should ideally begin to give a more timely estimate.


What level is the R number currently?


Firstly, the reproduction number is not an absolute and is an estimate. It also changes as our behaviour changes, or as immunity develops.

A group of researchers called Spi-M use multiple models to produce official estimations. As at the middle of June, the R number is between 0.7 and 0.9 for the whole of the UK, and between 0.7 and 1 for England alone.

However, research by Public Health England and Cambridge University suggests R is on the rise. R is now at around 1 for the south-west and just over 1 for north-west England.

Researchers at the London School of Hygiene and Tropical Medicine also say the overall R may be creeping up, and estimate the R in the south-west to be around 1 and 0.8 in the north-west.

Multiple research groups, including those at the University of Cambridge, have concluded that the R number has come down the most in London. Consequently, containing the virus most in that region. This may be a consequence of London being hit first and benefitting most from the tightest time in lock-down.

Epidemiologist Prof John Edmunds suggested that the R number is not stable and is in fact rising despite measures in place to lower it. He says:

“The large amount of community transmission that was occurring a couple of months ago has not come to a complete stop but has reduced enormously. The epidemic has been concentrated in settings such as care homes and hospitals, where infections spread efficiently, meaning they are now influencing the average R to a greater degree, and hence R appears to have crept up.”


What measures are in place to keep the R number low?


Governments everywhere want to instigate appropriate measures to control the spread of the virus and force the R number down.

This is the reason you’ve not seen family, have had to work from home and the children have been off school. Stopping people coming into contact with each other is vital to cut the virus’s ability to spread.

Initially, before the start of any measures, the R number was well above one and the conditions were ripe for an overwhelming outbreak. There was a real worry that the NHS might not be able to cope. Successive restrictions brought it down, but it was not until full lockdown that it was driven below one.

This shows that social distancing measures are working and we must continue to monitor the situation and avoid any unnecessary contact with other individuals where we could contract the virus or unwittingly pass it on.


Which measures could we lift?


Unfortunately, there is no confirmation of how much each intervention affects the virus’s spread, although there are estimates.

“Opening schools versus workplaces versus other gatherings – understanding how much they increase the R number, is going to be the challenge,” said Dr Kucharski.

Another issue is that people’s behaviour changes over time, so the number can creep up even if lockdown policies remain unchanged.

What we need is new ways of controlling the virus, such as more extensive testing and tracing or location-tracking apps.

These can suppress the R number in a more targeted way, allowing the lifting of some of the measures.

There are also serious worries as to how the mass gatherings and demonstrations that have occurred recently, may have spread the virus.


Will a vaccine help?


Having a vaccine is another way to bring down the reproduction number.

Scientists estimate that each coronavirus patient would naturally infect an average of three others, but if a vaccine could protect two of them from infection, then the reproduction number would fall from three to one.




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