Britain's R number plummeted when the lockdown was introduced

A mass testing scheme which will swab 100,000 people for coronavirus will have a 'huge impact' on when and how the UK comes out of lockdown.

In a nationwide effort to work out how fast the virus is spreading in Britain, scientists have embarked on an attempt to test tens of thousands of people and to begin long-term surveillance of COVID-19 cases and local outbreaks. 

Doing so will help them to calculate the reproduction number of the virus - known as the R value - which will then influence when lockdown measures can begin to lift.

Prime Minister Boris Johnson yesterday confirmed that the R is now lower than 1, meaning the virus is spreading slower than one-to-one and the outbreak is on course to come to a natural end.

At the start of the outbreak in the UK the R rate had been between 2.4 and 4, scientists say, but the dramatic stay-at-home measures that came into place on March 23 have cut it by at least two thirds.  

The virus cannot survive if the R remains below one, and the Government must now scale up its testing and surveillance to make sure it is never allowed to rise above that number again.

Carrying out hundreds of thousands of tests on people all over the country, regardless of whether they could have COVID-19, will now be vital moving forward.

Lord Ara Darzi, director of the Institute of Global Health Innovation at Imperial College London, said a scheme to swab test 100,000 people across 315 different areas of the country is now 'up and running' and early results are expected within 'a couple of weeks'.

This will be combined with routine testing on a randomly selected group of at least 25,000 people who will submit to regular swab tests to be analysed by the University of Oxford over the next year so scientists can track the virus over time. 

The Imperial College COVID-19 Response Team, which has been advising the Government, estimated in March that the global average R0 of the coronavirus was 3.87. As social distancing and lockdown took effect that number has now plummeted to below 1, potentially as low as 0.5, meaning the virus will die out naturally if this continues

The Imperial College COVID-19 Response Team, which has been advising the Government, estimated in March that the global average R0 of the coronavirus was 3.87. As social distancing and lockdown took effect that number has now plummeted to below 1, potentially as low as 0.5, meaning the virus will die out naturally if this continues

Lord Darzi said on BBC Radio 4 this morning that the mass testing project would provide a 'snapshot' of the current situation in the UK which could then be tracked.

He said: 'We'll be testing 100,000 people in 315 local authorities, randomly selected, and the snapshot will give us not just the R value on a national level but also a local community level, which is also critical.

'We are up and running, we've sent nearly 2,000 and it will take about a couple of weeks to get them all out and back. 

'And obviously we need to analyse these and inform policymakers because this will have a significant impact in terms of easing the lockdown.

'There's another study going on at Oxford in 20,000 households which will be repeat tests... so the combination of these two studies will be very informative in terms of moving into the next phase.'

HOW TESTING WILL TRACK THE VIRUS'S R VALUE AND MONITOR COVID-19

As it steps up surveillance of COVID-19 the Government is now moving into four major population testing schemes:

100,000 RANDOM TESTS

Imperial College London will oversee the two-part REACT programme (Real-time Assessment of Community Transmission).

The first part of this will be the 100,000 tests of random people in 315 different areas of the UK, to see how many of them are currently infected.

RANDOM ANTIBODY HOME TESTS 

Part two will be a rollout of at-home antibody tests, which can tell whether people have already had the disease and recovered. These will be given to 300 people for an initial trial and then rolled out to 10,000 people and then to 100,000 if it is successful.

The antibody tests will create a picture of how many people have had the virus already and may have immunity to it, meaning they won't catch it again, at least in the short-term. 

REGULAR SWAB TESTS FOR 25,000 

These two testing phases will run alongside two other long-term programmes announced last week as part of the Government's 'test, track, trace' plan.

At least 25,000 people will be enrolled into a scheme in which they will have regular swab tests taken at monthly intervals to see if they are infected at the time. This will continue for the next year and will be scaled up to include 300,000 people if it is found to be useful.

REGULAR ANTIBODY TESTING 

And further antibody testing will be rolled out to 1,000 households across the country in which people will give blood samples for analysis to test whether they have developed immunity to the virus.

Sir Patrick Vallance, Britain's chief scientific adviser, yesterday confirmed officials are using population testing and data on official cases of coronavirus to work out how fast the virus is spreading, signified by its R, or R0, value.

He said: 'At the moment we’re using a calculated R looking at all sorts of things including contacts, looking at genomics, looking at data from ambulances, hospital admissions, and so on, to calculate the R.' 

Lord Ara Darzi, director of the Institute of Global Health Innovation at Imperial College London, explained on BBC Radio 4 this morning: '[This] will be a snapshot of the R value across the country. We'll be testing 100,000 people in 315 local authorities, randomly selected, and the snapshot will give us not just the R value on a national level, but also a local community level, which is also critical.

'We are up and running, we've sent nearly 2,000 and it will take about a couple of weeks to get them all out and back, and obviously we need to analyse these and inform policymakers, because this will have a significant impact in terms of easing the lockdown.

'There's another study going on at Oxford in 20,000 households which will be repeat tests... so the combination of these two studies will be very informative in terms of moving into the next phase.' 

CONTACT TRACING 

As well as stepping up testing the Government will also employ an army of 18,000 contact tracers - likely to be repurposed civil servants - by mid-May.

These will be tasked with contacting people who have tested positive for the coronavirus and gathering details about the social networks around them, enabling them to isolate people who might have it and stop them spreading it further.

Prime Minister Boris Johnson put the R value at the heart of Britain's coronavirus battle at his Downing Street press conference yesterday when he revealed the Government's dedication to keeping it below 1.

It is currently estimated to be between 0.6 and 0.9, meaning every 10 people who get infected with the virus can be expected to transmit it to six to nine others.

This means that, as long as the reproduction number can be kept below 1, the outbreak will eventually run out of road and come to an end naturally.

Lifting lockdown measures, however, will cause it to rise and politicians are now under pressure to juggle the damage being caused by an economic shutdown with the damage that would be caused by a second outbreak and second lockdown.

Because so few people have had the disease and developed immunity, it is vital that the number of people currently infected drops as low as possible before lockdown lifts, to avoid those patients triggering another outbreak. 

Dr Kit Yates, senior lecturer in mathematical biology at the University of Bath and author of The Maths of Life and Death, told MailOnline: 'The reason we are holding on to complete lockdown for so long is because we want to bring cases down to a very low level and the quickest way to do that is to keep R as low as possible.'

He added: 'Until we actually go through the experiment of lifting the different restrictions we will not really know the effect on R. 

'You can expect a great deal of caution in the measures the government start to relax. Expect it to be conservative initially.' 

As it steps up surveillance of COVID-19 the Government is now moving into four major population testing schemes.

Imperial College London will oversee the two-part REACT programme (Real-time Assessment of Community Transmission).

The first part of this will be the 100,000 tests of random people in 315 different areas of the UK, to see how many of them are currently infected - this is the scheme Lord Darzi referred to.

Part two will be a rollout of at-home antibody tests, which can tell whether people have already had the disease and recovered. These will be given to 300 people for an initial trial and then rolled out to 10,000 people and then to 100,000 if it is successful.

The antibody tests will create a picture of how many people have had the virus already and may have immunity to it, meaning they won't catch it again, at least in the short-term. 

These two testing phases will run alongside two other long-term programmes announced last week as part of the Government's 'test, track, trace' plan.

At least 25,000 people will be enrolled into a scheme in which they will have regular swab tests taken at monthly intervals to see if they are infected at the time.

This will continue for the next year and will be scaled up to include 300,000 people if it is found to be useful.

And further antibody testing will be rolled out to 1,000 households across the country in which people will give blood samples for analysis to test whether they have developed immunity to the virus. 

The University of Bath's Dr Yates added: 'Looking at how numbers of cases are changing can give us a handle on the current value of R. 

'If we see cases are decreasing then this strongly suggests R is less than one. 

'Modellers can fit their models to the data on cases (or perhaps more reliably deaths) in order to reverse engineer the value of R that fits best. Hospital admission data can also give us an idea and are perhaps a little more reliable than testing figures.'

How Britain's R number plummeted when the lockdown was introduced and what it means for emerging from the other side

Prime Minister Boris Johnson last night put detailed science at the heart of Britain's coronavirus crisis and said the status of the lockdown now depends on the virus's reproduction number - known as the R. 

Watching the number of new patients and the rate at which it goes up or down will be the best way officials can monitor how quickly the virus is spreading, which will in turn guide which risks the Government feels it can take in lifting lockdown.

The data that lays out Britain's R value will shape the lives of everyone in the UK over the coming weeks and months, and MailOnline here explains how: 

What is the R number? 

Every infectious disease is given a reproduction number, which is known as R0 - pronounced 'R nought' - or simply R.

It is a value that represents how many people one sick person will, on average, infect.

Most epidemiologists - scientists who track disease outbreaks - believe the SARS-CoV-2 virus, which causes COVID-19, has an R value of around 3.

But some experts analysing outbreaks across the world have estimated it could be closer to the 6.6 mark.

Estimates of the R vary because the true size of the pandemic remains a mystery, and how fast the virus spreads depends on the environment. 

As an outbreak progress the R may simply be referred to as R, which means the effective rate of infection - the nought works on the premise that nobody in the population is protected, which becomes outdated as more people recover. 

How does the reproductive rate compare to other infections? 

SARS-CoV-2 is thought to be at three times more contagious than the coronavirus that causes MERS (0.3 - 0.8).

Measles is one of the most contagious infectious diseases, and has an R0 value of between 12 and 18 if left uncontrolled. Widespread vaccination keeps it suppressed in most developed countries.

Chickenpox's R0 is estimated to be between 10 and 12, but this is controlled in the UK by herd immunity. So many people catch it as children and become immune to reinfection that it is unable to spread among adults.

Seasonal flu has an R value of around 1.5 but it mutates so often - there are often one or more new strains each year - that people cannot develop total immunity to it. Recovering from one strain of flu does not protect someone from others.  

Ebola has an R0 of between 1.4 and 1.8 - this is low but it has so far only spread in countries with poor health facilities and its extremely high death rate (50 per cent) makes it a threat.   

Mumps has an R0 of between 10 and 12, making it highly infectious, but the measles vaccine (MMR) protects most people in Britain from catching it.

The R0 for whooping cough, known medically as pertussis, is estimated to be 5.5. The NHS urges mothers to have the pertussis vaccine during pregnancy because they are able to pass immunity on to their baby naturally.

How is it calculated? And can scientists ever be sure of the number? 

The R is not a set number and scientists calculate it by studying how fast the virus spreads in its perfect environment and also in society.

While the biology of the virus and the

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