The number of people in England who tested positive for coronavirus rose by 43% in a week, according to the latest test-and-trace figures, providing further evidence of a rise in infections.
The NHS statistics show that 9,864 new people tested positive in the week ending 2 September, the highest weekly number since test and trace was launched at the end of May.
The government said there had been 2,919 cases of coronavirus across the UK in the previous 24 hours – the third day in four that the total had neared 3,000 cases. Until the recent increase, the last time the daily total was above 2,000 was in May.
The proportion of close contacts who were reached and asked to self-isolate in England dropped to a new low of 69.2%, according to the latest test and trace figures. While the number has been relatively stable since mid July, it stood at 91.1% when test and trace was first launched.
James Naismith, professor of structural biology at the University of Oxford, said the figures suggested there was a real increase in infections, not just that more testing was yielding more positive results. “We are nowhere near the exponential growth seen in March, but the virus is building; this is worrying, given winter is coming,” he said. “It is disappointing that satellite test centre delays are growing. This suggests that this part of the testing system is starting to show very significant strain. Information is only useful if it is rapid enough to do good.”
He also said that given “there seems to be no lack of demand for testing”, it was puzzling that testing capacity in the UK was said to be 2.5m per week, while the number of tests processed is 1.3m a week. Ministers have said the problem with testing lies with capacity at labs.
Boris Johnson, who announced plans for “moonshot” mass testing on Wednesday, had previously pledged to get coronavirus test results delivered within 24 hours by the end of June. The latest figures show that remains some way off.
While the proportion of in-person test results received within 24 hours in England was up on the previous week, it was still just 61.9% . Including home test kits and satellite test centres, the figure was 29.7%.
Dr Daniel Lawson, a lecturer in statistical science at Bristol University, said: “We must get the infection number per infection [R number] below one to prevent a large second wave which will be impossible to prevent reaching vulnerable populations.
R, or the ‘effective reproduction number’, is a way of rating a disease’s ability to spread. It’s the average number of people on to whom one infected person will pass the virus. For an R of anything above 1, an epidemic will grow exponentially. Anything below 1 and an outbreak will fizzle out – eventually.
At the start of the coronavirus pandemic, the estimated R for coronavirus was between 2 and 3 – higher than the value for seasonal flu, but lower than for measles. That means each person would pass it on to between two and three people on average, before either recovering or dying, and each of those people would pass it on to a further two to three others, causing the total number of cases to snowball over time.
The reproduction number is not fixed, though. It depends on the biology of the virus; people’s behaviour, such as social distancing; and a population’s immunity. A country may see regional variations in its R number, depending on local factors like population density and transport patterns.
Hannah Devlin Science correspondent
“Proper widespread testing – not just of suspected cases, but of the general population – is key to catching outbreaks before they get out of control, though may be being implemented too late.
“Track and trace is also important. Although testing time at testing centres and mobile testing units is stable, home test kits and satellite test centres are dangerously slow – taking over three days on average – which will prevent proper test-and-trace response.”
Dido Harding, the interim executive chair of the National Institute for Health Protection, said: “We are doing more testing for the British public than other comparable European countries and we are adding thousands more tests a day. The figures show we have seen a significant increase in the demand for tests, but given the concerning rise in cases over the last couple of days, it is still vital for anybody who has symptoms to book a test and follow the advice you receive if you are contacted by NHS test and trace.”
