NHS Test and Trace is now reaching less than 50 per cent of the contacts of those who have had a positive test result for coronavirus, new analysis shows.
Statisticians said the latest official data revealed that the reach of the system dropped to 45 per cent in the week ending July 29, compared to 51 per cent the week before. This is despite a 17 per cent increase in positive cases, which is only partially explained by an increase in testing.
In the previous week, the system managed to interview 81.4 per cent of people who tested positive, nearly all of whom named contacts. Of these, 75.1 per cent were reached, giving an overall reach of just over 50 per cent.
However, for the latest week, 79.4 per cent of positive cases were interviewed and, of the contacts named, only 72.4 per cent were reached, giving an overall reach of 45 per cent.
Professor Chris Bonell, of the London School of Hygiene and Tropical Medicine, said: "The new figures for England are disappointing in that they are slightly less than those for the previous week. The figures for Wales are not directly comparable, but look a bit better."
The news came as Boris Johnson, the Prime Minister, described NHS Test and Trace as "world-beating" (see video below).
Keith Neal, emeritus professor of the epidemiology of infectious diseases at the University of Nottingham, said: "One persistent problem is that one in five cases, who should be at home and self-isolating, fail to be contacted by the contact tracers despite multiple attempts.
"These people have arranged a test and been informed of a positive result and expect to be contacted. It would be useful to have more information on these people as to why they are not participating in control measures.
"Not being able to trace contacts is understandable, but the cases could help in letting their contacts know."
Meanwhile, Dr Joshua Moon, research fellow in the Science Policy Research Unit at the University of Sussex Business School, said: "Cases are going up faster than testing – this is not a good sign.
"Over the nine weeks of NHS Test and Trace activity, the percentage of non-household contacts has been increasing, indicating that the changes are likely to be as a result of the Government's decision to relax lockdown measures."
Baroness Dido Harding, who runs NHS Test and Trace, said: "NHS Test and Trace is working. It has already helped to prevent almost a quarter of a million people unknowingly spreading the virus.
"But we do not work alone. Close partnerships with local government and public health teams are essential to stop the spread of the virus, and NHS Test and Trace continues to work hand-in-hand to support communities experiencing spikes in cases, through increased testing and additional contact tracing."