Contact tracing may cut the coronavirus R rate by as little as 2%, Test & Trace chief Dido Harding admits in letter to MPs
- Report said contact tracing impact is ‘relatively small’ and not likely to improve
- Overall, test, trace and isolate may cut R rate by up to 33%, Harding said
- But contact tracing makes up a tiny percentage; critics questioned its budget
- Baroness Harding already admitted 20,000 people per day may refuse to isolate
Contact tracing reduces the speed of the coronavirus’s spread by a maximum of five per cent and as little as two per cent, NHS Test and Trace boss Dido Harding has revealed.
Baroness Harding said in a report to Parliament’s science committee that the act of tracking down people who have been close to Covid-19 cases has only a ‘relatively small’ effect on the R rate of the virus.
The R rate measures how many people each infected person passes the virus on to before they recover. It must stay below 1.0 if an outbreak is to stop growing.
The letter, published today, estimates that the UK’s entire test, trace and isolate system would keep the R down by between 18 and 33 per cent in a scenario similar to October 2020, when there were an average of 19,000 cases per day.
It became less effective when the outbreak got bigger in November, December and January, and when the fast-spreading new variant took over, Baroness Harding admitted.
She said: ‘The impact of contact tracing alone reduced the R number by 2-5% (with testing and self-isolation accounting for the remaining 16-28%).’
If the R rate were 0.9 – the maximum value for the UK now, as estimated by SAGE on Friday – a two per cent reduction would cut it to 0.882. A five per cent drop would cut it to 0.855.
In a report published alongside the letter Test and Trace chiefs said it was unlikely the service would improve on this, saying: ‘The impact of contact tracing is relatively small. Even with small changes or improvements to the model, it is not expected that the impact of contact tracing will change drastically. It would remain of the same order of magnitude.’
The admission led critics to question whether NHS Test and Trace’s eye-watering £22billion budget is good value for money.
Baroness Dido Harding said in a letter to the Parliament Science and Technology Committee that contact tracing specifically may only lead to a 2-5 per cent reduction in the R rate
Baroness Harding’s letter said: ‘Our modelling was based on the combination of testing, tracing and self-isolation in an October-like prevalence environment and compared to a scenario with only social distancing restrictions and no self-isolation.
‘The model estimates that the combination of testing, tracing and self-isolation in October 2020 resulted in an R reduction of 18-33 per cent, compared to a scenario with only social distancing restrictions and no self-isolation.
‘The impact of contact tracing alone reduced the R number by 2-5 per cent (with testing and self-isolation accounting for the remaining 16-28 per cent).
‘An 18-33 per cent reduction corresponds to a reduction in the R number of 0.3-0.6, given the official estimate in October 2020 was around 1.2
‘If NHS Test and Trace were to meet the operational targets it set in the Business Plan, and circumstances otherwise were similar to October 2020, the model estimates that transmission would reduce by 33-42 per cent.
‘Here, the impact of contact tracing alone would contribute a 7-10 per cent reduction in the R number.’
Around 20,000 people every day are flouting instructions to self-isolate, the government’s testing tsar admitted on February 3.
Baroness Dido Harding gave the staggering estimate – and conceded it could be even higher – as she was grilled by MPs.
Amid rising anxiety that the lack of compliance with the Test & Trace system could hamper efforts to control the virus, the peer said evidence suggested 20 per cent of the 100,000 cases and contacts identified every day did not fully obey the rules.
Lady Harding highlighted a range of potential reasons including money worries, not having help from people to obtain food and other essentials, or just finding the isolation too oppressive.
However, she defended the performance of the Test & Trace scheme despite it failing to hit targets, saying it is on track to reduce the crucial coronavirus R rate by between 0.6 and 0.8 in hospots, but can only ever be ‘one element’ of the response.
The comments came as Lady Harding was questioned by a joint session of the Commons health and science committees.
Quizzed by health committee chair Jeremy Hunt, she gave the rough figure of 20,000 a day breaching isolation, but added that her ‘biggest concern’ was many more people did not come forward for testing.
Asked why she thinks people are not isolating when they should be, Lady Harding said one element is communication – people not understanding and not being clear about what they should and should not do.
She said: ‘The clearer and simpler the guidance, the easier is it for people to follow it.’
The Tory peer said the second element is people finding it ‘practically impossible’ – not having enough food in the fridge, having care responsibilities, having to collect a prescription.
The benefits of the hugely expensive contact tracing system, which is part-run by contractors’ call centres and part-run by local councils, have long been debated.
There are concerns that the system is too slow to find the at-risk contacts and warn them they might be infectious, and that people don’t follow tracers’ instructions.
The way the system generally works is that, once someone has tested positive for coronavirus, they are logged in a database and asked to give details of all the people they were in contact with shortly before their positive test.
Those contacts are then phoned by contact tracers who tell them they are at risk and ask them to self-isolate for 10 days.
But Baroness Harding herself admitted this month that as many as 20,000 people per day may be refusing to follow this advice and continuing to go out to work.
Self-isolating can leave people out of pocket if they are paid by the hour or day, meaning many cannot afford to stay at home, despite NHS Test and Trace now offering a £500 payment to people on low incomes.
Baroness Harding said in a meeting with the science committee earlier this month that evidence suggested 20 per cent of the 100,000 cases and contacts being identified each day at the peak of the second wave did not fully obey the rules.
She highlighted a range of possible reasons including money worries, not having help to get food or other essentials, or just finding the isolation too stifling.
Baroness Harding admitted in today’s letter that this willingness to co-operate – or lack of it – might be limiting the success of the contact tracing programme.
On other aspects holding it back, she wrote: ‘Changes to prevalence, national restrictions and the emergence of new variants mean the real world has changed significantly compared to the “October like environment” the model simulates.’
Scientists have called into question the astronomical budget that Test and Trace gets to run the service and whether the cash allocated to private firms to do contact tracing is good value for money.
Professor David Spiegelhalter, a statistician at Cambridge University, said in a tweet: ‘They estimate R reduction of 18-33% compared to a scenario with only social distancing restrictions and no self-isolation – but nearly all due to isolation: contact tracing alone reduced the R number by only 2-5%.
‘So could funds for centralised contact-tracing be better used?’
Dr Kit Yates, a mathematician at the University of Bath, added: ‘I can’t help thinking that some of the £22 billion – the figure widely quoted as having been earmarked for the operation thus far – might be better spent on providing support for isolation, which is likely to have a significant impact reducing transmission.’
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