Data from Covid-19 symptom tracking app puts R value at around 1 – expert

The R number of coronavirus transmission is falling and may be around 1, an expert has claimed.

New data from the Covid Symptom Tracker app, which is run by King’s College London (KCL), suggests there has been a slight drop in new Covid-19 infections across England, Wales and Scotland.

Professor Tim Spector, who leads the app study, said on Twitter today: “More good news as the Zoe CSS app survey continues to show a plateauing and slight fall in new cases in England, Wales and Scotland with an R of 1.0.”

He added that the reason the NHS is concerned is because “while rates may be starting to come down in children and the younger adults – there is a slow rise in the over-60s who are more likely to go to hospital – so we can’t relax”.

R, which stands for reproduction number, represents the average number of people each Covid-19 positive person goes on to infect.

When the figure is above 1, an outbreak can grow exponentially, but if it goes below 1, it means the outbreak is shrinking.

The data from KCL’s symptom tracker app appears to differ from the figures published last Friday by the Government Office for Science and the Scientific Advisory Group for Emergencies (Sage), which estimates R to be between 1.1 and 1.3.

The figure is slightly lower than Sage’s official estimate from the previous week, which stood at between 1.2 and 1.4.

A Government adviser said that while the R number appears to be falling, it is still above 1 – which means “we are still looking at a growing epidemic”.

The official estimate also differs from one put forward by Imperial College London as part of the REACT-1 study last week, which is around 1.6 for England.

Meanwhile, KCL said that the data from its app suggests the number of daily new Covid-19 cases in the UK is steadily increasing, but it is “not surging as other sources have suggested”.

This data is based on around a million weekly users self-reporting symptoms and swab test results.

The estimate comes as Boris Johnson told the Cabinet on Tuesday there is “light ahead” in the battle against coronavirus.

The Prime Minister said the R was “only just above one” and the lockdown would bring it back below that threshold.

New data from the MRC Biostatistics Unit at the University of Cambridge puts the R number above 1 in most regions.

The group estimates that the daily number of new infections each day across England is 77,600.

It said the daily number of new infections is particularly high in the Midlands, the North West, the North East and Yorkshire.

The scientists predict the number of deaths each day is likely to be between 380 and 710 by November 14.

Lead researcher Professor Daniela De Angelis, deputy director at the MRC Biostatistics Unit, said: “R values are slowly decreasing, but they remain above 1 in all regions.

“The number of infections has increased to around 80,000 per day and will continue to increase, leading to steep rise in mortality in the near future.

“Curtailing this transmission requires sustained social distancing interventions. We welcome the new measures announced on the 31st of October.”