The U.K. Prime Minister Boris Johnson said in a recent Downing Street press briefing that there is an increasing need to ensure that the R-value of coronavirus remains less then 1 if the countries are to ease lockdown to restore the economy.

Many governments across the world are being guided by the “R rate” to ward off COVID-19 pandemic. However, not everyone is aware of what the R-value is.

R0, pronounced as R-naught, refers to the reproduction number of a pathogen and it helps estimate how dangerous the outbreak is likely to be and how fast it is likely to spread.

To the governments across the world, this number helps understand what should be the duration of lockdown to prevent potential COVID-19 spread among the general public and what measures should the decision and policymakers take to reduce the burden of the pandemic.

R0 value indicates how many people an infected person is likely to spread the infection. A number greater than one indicates that the infection is likely to spread, while a number less than one indicates that the infection is most likely to fizzle out. 

An R0 value is equivalent to 1 means that every infected person is likely to cause one new infection. The disease remains stable in this case and does not result in an outbreak.

The R0 rate may vary from one infectious disease to the other. For example, measles is R15, which means that its reproduction rate is extremely high and can cause massive outbreaks.

What is the R rate for coronavirus?

The reproduction rate tends to change with the spread of an infection as there are fewer people who are at risk. Also, the R-value keeps on changing because of the restrictions and interventions that are put to slow down disease spread.

Therefore, our behavior dictates the reproduction rate of coronavirus and so does the immunity that people develop against it over some time.

Mathematical modelers at Imperial College London are currently trying to deduce numbers on how lockdown measures in the U.K. have affected the reproduction rate of coronavirus.

They know that before any measures were kicked in, the R rate for coronavirus was more than one. But after social distancing measures and a full lockdown was imposed, the number went below one. However, they prefer using the tern Rt instead of R0 or R1 because it keeps on changing with the introduction of new measures and as restrictions are lifted off.

"Let me just emphasize that keeping the R down is going to be absolutely vital to our recovery, keeping the reproduction rate of the disease down, and we can only do it by our collective discipline and working together,” Johnson said during the briefing. "I know we can do it, because we did it, we've shown we can do it, in phase one of this disease.

UK Prime Minister Boris Johnson Prime Minister Boris Johnson leaves 10 Downing Street for PMQ's on March 25, 2020 in London, England. British parliament will be suspended tonight due to concerns about the spread of COVID-19. It had previously been scheduled to break for Easter on March 31; it will tentatively sit again on April 21. The Coronavirus (COVID-19) pandemic has spread to at least 182 countries, claiming over 18,000 lives and infecting hundreds of thousands more. Peter Summers/Getty Images