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The COVID-19 R number, what is it?

The COVID-19 R number, what is it?

The R-value of COVID-19 and any other infectious disease refers to its ‘reproduction’ number. It is a number which enables countries to determine the disease’s ability to spread. This number shows how many people one person will pass the virus onto on average. Therefore, if the R number is 3 then one person can pass it onto three more people who can then pass it on to three more people and so it goes on.

The R number is calculated by working backwards; professionals use data such as how many people are dying; how many have been in hospital and how many have tested positive to see how easily the virus is spreading.

The R number will generally reflect the level of reproduction two to three weeks before it is given. So, for example, if the R number is given as 0.5 on the 21st of May, this represents the R number from around the 1st – 7th May.

Ideally, to try and control a virus, the R number needs to be below 1. If the number is higher than 1 then the number of people infected increases exponentially and will continue to increase. However, when the number is lower than 1, this means that the disease will eventually die out as not enough people are being infected to sustain the outbreak.

In the UK, prior to lockdown, it was estimated that the R-value was as high as about 3 – 4. After the first phase of lockdown, it was thought to have reduced to somewhere between 0.5 – 0.75.

The R-value is not necessarily the same in all parts of the same country as this can depend on many factors such as how seriously lockdown restrictions were adhered to. In the UK, the North-East is thought to have the highest overall R-value, but this can and does change.

The R-value is significant because it informs countries about how and when they can lift their lockdowns. The aim of lifting a lockdown is to ease restrictions so that some sense of normality is returned whilst keeping the R-value below 1, which is not a comfortable balance to strike.