What do R1 and R0 Infection Rate Numbers Mean and How Do They Relate To Coronavirus?

Governments across the world are being guided by what they call the "R rate" when it comes to fighting the COVID-19 pandemic.

It can determine how long lockdowns last and what measures are adopted as policymakers seek to stop the spread of the virus.

So what is the "R rate" and what does it mean?

R0, pronounced R-naught, relates to the reproduction number and is used to gauge how likely the outbreak is to spread.

It refers to the number of people that one infected person will pass the virus on to, on average.

"It's important to appreciate that R0 is not a fundamental property of the disease," Kit Yates, senior lecturer in mathematical biology at the University of Bath, has told Newsweek.

R0 is considered important because if it's greater than one, the infection is likely to keep spreading. If it's less than one, the outbreak is likely to peter out.

The R rate in coronavirus pandemic
The R0 rate helps government understand how likely the pandemic is to spread Getty

Measles, for example, has one of the highest R numbers, with a reproduction number of 15. It can cause explosive outbreaks.

"As the disease progresses, the reproduction number changes as there are fewer susceptible people to infect," Yates said.

"It also changes due to the interventions we put in place to slow the spread of the disease. Once the disease is in full flow we tend to call it R, the 'effective reproduction number' or just the "reproduction number.'"

At a Downing Street press briefing, Prime Minister Boris Johnson stressed the need to keep the R value low, if the country is to begin easing restrictions to emerge from the lockdown.

Johnson explained that if the number is above one then it means for every single coronavirus case, an individual is likely infecting an average of at least one other person.

The prime minister said: "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.

"I know we can do it, because we did it, we've shown we can do it, in phase one of this disease.

"This country came together in a way few of us have seen in our lifetimes."