In Depth

What we need to do to make track-and-trace work

New study sets out new goals for the UK’s widely criticised coronavirus contact-tracing system

Boris Johnson promised back in May that the UK would have a “world-beating” contact-tracing system, yet the scheme has been plagued by delays and setbacks.

Last night, Professor John Edmunds, who sits on the Scientific Advisory Group for Emergencies (Sage), said the system is still ineffective.

“I honestly couldn’t care less whether it’s world-beating or not,” he told BBC Newsnight.

“I just wanted it to be virus beating and it is not. The system is quite clunky, it takes quite a lot of time to get the information out of individual cases about their contacts.”

What numbers would add up to success?

Another group of scientists published research yesterday in The Lancet that sets out the minimum standards that need to be met in order to avoid a second wave of Covid-19 infections.

The model - based on a London School of Hygiene and Tropical Medicine (LSHTM) analysis of infection rates and social interactions - suggest that the NHS would need to identify 75% of people with symptomatic Covid-19 and then trace and isolate 68% of their contacts.

Alternatively, if 87% of symptomatic infections were identified, only 40% of contacts would have to be traced. 

The World Health Organization (WHO) defines a contact as anyone who has direct contact with a Covid-19 carrier or spends more than 15 minutes within one metre of them.

How many people are we testing and tracing?

Based on latest infection figures, the Office for National Statistics (ONS) estimates that about 4,200 people are contracting Covid-19 in England each day, and that about 33% of these cases are symptomatic. This equates to around 1,400 symptomatic infections per day.

However, positive tests are currently running at just over 700 per day in England, which implies that only about 50% of people with the disease are being tested.

Of those who do test positive, about 81% are reached by contact tracers, according to ONS data, and 75% of their contacts have been contacted and asked to self-isolate - which implies that about 60% of all contacts are traced.

Those figures - 50% tested and 60% traced - are significantly below the mimums implied by the LSHTM model.

It is also unclear how many people comply with requests to self-isolate. “NHS Test and Trace has no data on how many of those contacted follow rules as it does not carry out follow-up calls,” the Daily Mirror reports.

That said, the failure of the system is not a certainty. “Like all models, it is a crude approximation of the real world, which is only as good as the assumptions it makes,” says The Spectator

But Edmunds and the LSHTM team are not alone in identifying room for improvement.

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