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Quick and effective testing and tracing could reduce the coronavirus R number by up to 26%

The UK’s coronavirus reproduction rate could be slashed by a quarter with quick and effective testing and tracing, a study suggests.

Scientists estimate Britain’s R value is currently hovering between 0.8 and the dreaded number 1, the level at which the epidemic could spiral back out of control.

But Imperial College London researchers said if the NHS Test and Trace system was up to scratch it could definitely be squashed below the danger zone. 

According to their mathematical modelling, the R – the average number of people each coronavirus patient infects on average – could be shrunk by 26 per cent if 80 per cent of Covid-19 cases and their contacts are tested and isolated in 24 hours. 

However, the UK’s sluggish contact tracing system is still struggling to hunt down almost half of infected people’s contacts. 

Official statistics also show that only around two-thirds of people who get swab tests received their result within 24 hours, down from 76.9 per cent last week. 

Prime Minister Boris Johnson had promised to have this figure at 100 per cent by July.

A total of 52,735 people who tested positive for Covid-19 in England have had their cases transferred to the NHS Test and Trace contact tracing system since its launch, according to figures from the Department of Health and Social Care.

Of this total, 41,254 people (78.2 per cent) were reached and asked to provide details of recent close contacts, while 9,938 (18.8 per cent) were not reached.

A further 1,543 people (2.9 per cent) could not be reached because their communication details had not been provided.

In the most recent week, the service successfully contacted 79.7 per cent of infected people, which was down from 80.5 per cent a week earlier.

Slightly more of the at-risk contacts were reached – 61.1 per cent in the week ending August 5 – up from 60.9 per cent a week before.

However this still means that four out of 10 people who are at risk of having caught Covid-19 from an infected person are not being warned by the Government.

In a thinly-veiled jab at the UK’s current tracing system, Professor Nicholas Grassly, from Imperial’s School of Public Health, which conducted the recent study, said: ‘Effective testing is key to controlling the coronavirus pandemic.

‘We need to use testing to prevent transmission in two ways – first, to identify infected individuals and their contacts to reduce transmission through isolation and quarantine, and second, to detect outbreaks so that local lockdowns can be applied when needed. 

‘Our results show that test and trace can help reduce the R number but needs to be carried out effectively and quickly to do so. 

‘Test and trace alone won’t be enough to control transmission in most communities and other measures alongside will be needed to bring the R number below one.’  

The researchers developed a mathematical model of SARS-CoV-2 transmission based on infectiousness and PCR test sensitivity over time since infection. 

According to this, if everyone with symptoms compatible with Covid-19 self-isolated and self-isolation was 100 per cent effective in reducing onwards transmission, self-isolation of symptomatic individuals would result in a reduction in R of 47 per cent. 

Weekly screening of healthcare workers and other high-risk groups, irrespective of symptoms, by use of PCR testing is estimated to reduce their contribution to SARS-CoV-2 transmission by 23 per cent, on top of reductions achieved by self-isolation following symptoms, assuming results are available within 24 hours. 

Dr Margarita Pons-Salort, from Imperial’s School of Public Health, said: ‘We looked at how testing can be used to control transmission. 

‘Although regular screening of asymptomatic individuals in high-risk groups, as well as contact tracing (test-trace-isolate) of the wider population can help reduce transmission, control of Covid-19 cannot rely on these strategies alone. ‘

Among others, the effectiveness of these strategies depends a lot on the timeliness to provide test results and to find and quarantine contacts. 

‘This means that to have a real impact on transmission, testing strategies need to be implemented very well.’

The research, published in Lancet Infectious Diseases, was supported by the UK Medical Research Council.  

It comes after the much-delayed NHS Test and Trace smartphone app was re-launched last week, with a second round of trials on the Isle of Wight and in the London borough of Newham.

England’s beleaguered app, of which the first version had to be scrapped in June after a string of failures, has now been recreated using technology made by Google and Apple.

Officials are rolling out trials of the app – which was originally slated for release in mid-May – to some staff in the NHS and residents of the two areas to test whether it is good enough to use nationwide.  

If it is found to work, it will be used alongside the human contact-tracing system which is based on call centres and local councils visiting people’s homes.

Bluetooth technology will keep a record of which phones spend 15 minutes within 2metres (6’7″) of one another and then alert people if they have been near someone who later tests positive for Covid-19.

Users will also have an ‘isolation companion’ which has countdown timer if someone has to self-isolate, and will be able to ‘check in’ to places such as pubs and restaurants using QR codes.

They will also be shown what the risk level is in their local area based on the first half of their postcode, with places being categorised as low, medium or high risk.

The app will rely totally on members of the public co-operating, volunteering to let it track their connections and following the instructions it gives them on getting tested and self-isolating.

Despite efforts to iron out flaws in the technology, the Department of Health has admitted that around half of people who are warned they have been near an infected person will actually not have been within the 2m for 15 minutes danger window.

And three out of 10 people who were put at risk – 31 per cent – won’t receive a notification at all. In trials it had a 69 per cent accuracy rate at detecting people who had been at risk, and it was 55 per cent accurate at detecting people who had not.  

The newest version of the app is being launched after the first attempt was abandoned in June because it did not work on Android smartphones.

The NHS’s app — which was originally promised for mid-May and the NHS spent months developing — was unable to spot 25 per cent of nearby Android users and a staggering 96 per cent of iPhones in the Isle of Wight trial.

This was because the Bluetooth system developed by the NHS effectively went into ‘sleep mode’ when the phone screens were locked and developers couldn’t fix the glitch.

Different Bluetooth technology made by the phone manufacturers Apple and Google themselves has turned out to be significantly better at detecting other phones.

Officials said the app software now reliably detects 99.3 per cent of nearby app users, regardless of what type of phone they have.

And it will use, on average, two to three per cent of a phone’s battery life each day, officials say.

Another major difference between the two is that Apple and Google’s technology stores the anonymously log of someone’s contacts entirely in the phone – it is never shared with anyone else and can be deleted at any time – whereas the NHS’s worked on a system which meant it had to be sent to a centralised database.

Officials have changed this to squash concerns about privacy, now insisting the app ‘tracks the virus, not people’.

In another improvement to the privacy afforded by the app, it will have a toggle switch for people to turn the contact tracing on or off without uninstalling the app.

People can choose at any time to make the app stop recording connections to other phones.

And the app will now not send any information to the NHS or the Government – people will only be given advice to self-isolate if they are at risk, or advised to get a test if they have symptoms.

People will have to report a positive test themselves in order to alert people they may have put at risk.

Once hailed as a vital part of the contact tracing system, the app is now an addition to the human system, officials say.

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