Effective test and trace could 'reduce coronavirus R rate by up to 26%'

18 August 2020, 23:56

An effective test and trace could reduce the R value by up to 26 per cent
An effective test and trace could reduce the R value by up to 26 per cent. Picture: PA

By Kate Buck

An effective test and trace system could educe the R value by up to 26 per cent, a study has suggested.

But Imperial College London researchers warn that testing alone is unlikely to bring the R number below one at current levels of immunity.

Therefore other interventions such as continuing physical distancing will be needed, they say.

The R number represents how many people someone infected with Covid-19 is likely to go on to infect.

In the study, researchers from Imperial's Covid-19 Response Team looked at the potential impact of different testing and isolation strategies on transmission of the coronavirus.

An effective test and trace system depends strongly on the coverage of testing and the timeliness of contact tracing, they say.

Baroness Dido Harding, executive chairwoman of NHS Test and Trace
Baroness Dido Harding, executive chairwoman of NHS Test and Trace. Picture: PA

According to the study, if 80 per cent of cases and contacts are identified and there is immediate testing following symptom onset and quarantine of contacts within 24 hours, then the R number could potentially be reduced by up to 26%.

However, the researchers say the test and trace system in the UK is currently falling short of that.

Professor Nicholas Grassly, from Imperial's School of Public Health, said: "Effective testing is key to controlling the coronavirus pandemic.

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"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."

Last week, NHS Test and Trace figures showed that, in the 10 weeks since the launch, 81.5% of contacts had been reached and asked to self-isolate.

Some 18.5% of contacts were not reached.

Researchers say optimal testing strategies should include regular screening of high-risk groups such as health and social care workers during periods of sustained transmission.

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