What is the R value? Covid-19 infection rate explained - and how low it needs to be before lockdown can lift
As the UK approaches its next lockdown review on 7 May, many will be keen to know if it is possible to start easing restrictions
While details of an “exit strategy” are yet to be announced, the government has said it needs to be satisfied of five key things before considering it safe to adjust the current measures.
One of these is the R value, or rate of infection. But how is this measured, and when will it be low enough to ease lockdown?
What is the ‘R’ rate?
The “R” value, or infection rate, refers to the number of people that one infected person will pass the virus to on average.
Coronavirus has an estimated reproduction number of three, meaning an infected person will likely pass the virus on to at least three other people.
A reproduction number that is higher than one poses a significant risk, as the number of cases can increase rapidly, making it harder for the spread to be contained.
However, if the number is lower than one, the virus will eventually die out as not enough new people are being infected to sustain the outbreak.
What is the current ‘R’ rate?
The ‘R’ rate in the UK is now thought to be somewhere between 0.5 and one.
This means that each infected person will pass the virus on to fewer than one person, and as a result, the total number of cases is now starting to fall.
But if the ‘R’ rate rises above one, it could lead to another exponential rise in infections.
Speaking at a Downing Street press conference on Thursday (30 Apr), Boris Johnson stressed the importance of keeping the UK’s ‘R’ rate low, stating it is key in bringing the country out of lockdown.
Mr Johnson said: "Let me just emphasise 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.
"To protect the NHS and to save lives, and that’s why I am absolutely convinced we can do it in phase two as well."
Sir Patrick Vallance, the government’s chief scientific officer, added that it is “highly likely” the R value has been reduced to below one as a result of the imposed lockdown measures.
How will the ‘R’ rate help to lift lockdown?
The rate of infection is one of the government’s five tests that need to be met before it is deemed safe to ease the current restrictions.
The ‘R’ rate must have decreased to manageable levels across the country before measures can be lifted, meaning the value must fall below one.
It is believed the rate is now between 0.5 and one, meaning infections are now at a manageable level.
These are all five tests that need to be met before considering a lifting of lockdown:
– Protect the NHS’s ability to cope and be confident that the NHS is able to provide sufficient critical care across the UK
– A sustained and consistent fall in daily death rates to be confident the UK is beyond the peak
– Reliable data from government scientific advisers showing rate of infection is decreasing to manageable levels across the board
– Confidence that testing capacity and personal protective equipment (PPE) are in hand with “supply able to meet future demand”
– Confidence that any adjustments to the current measures would not risk a second peak in infections.
Mr Johnson said: “When we are sure that this first phase is over and that we are meeting our five tests: deaths falling, NHS protected, rate of infection down, really sorting out the challenges of testing and PPE, avoiding a second peak, then that will be the time to move on to the second phase in which we continue to suppress the disease and keep the reproduction rate – the R rate – down, but begin gradually to refine the economic and social restrictions and one-by-one to fire up the engines of this vast UK economy.
“And in that process, difficult judgments will be made and we simply cannot spell out now how fast or slow or even when those changes will be made, though clearly the Government will be saying much more about this in the coming days.”