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COVID-19 infection
by Rod Tucker
Published on 23 February 2021

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COVID Symptom study suggests falling UK COVID-19 infection rates are plateauing

One source of data on the incidence of COVID-19 cases comes from the smartphone-based app used in the COVID Symptom study. While the latest data are aligned with other sources, indicating that infection rates have fallen, this drop appears to have slowed and is beginning to level off.

The REACT-1 study conducted by a team from Imperial College, London, provides a regular snapshot of the prevalence of COVID-19 across the UK over a two-week period. The data are based on the results of nose and throat swabs, obtained from a random sample of the population. The latest data which covers the period up to 13 February 2021, is based on a sample of 85,473 swab results, of which 378 were positive, giving a weighted prevalence of 0.51% compared to 1.57% in the previous analysis that covered January 2021. Similarly, the Office for National Statistics (ONS) undertakes a weekly random sample (also based on nose and throat swabs) and their latest data, covering the period up to 12 February 2021, estimates that 1 in 115 people have symptomatic COVID-19, which again, is lower than their previous estimate from January 2021. The COVID symptom study collects self-reported symptomatic data on a daily basis via a smartphone app. As such this is the most up-to-date source of information on infection trends, whereas both REACT-1 and the ONS data provide an estimate of prevalence over a slightly longer period of time.

The latest COVID symptom data, which is based on around 1 million weekly reporters, estimates that there are 14,064 daily new symptomatic cases. This equates to a much lower prevalence of 1 in 294 people in the UK. While these data are more encouraging, suggesting that the rate of infection is falling even more than the estimates from either the REACT-1 or the ONS, the symptom study does show that the fall in new cases has actually started to slow and even plateaued. Using the app data, the group estimating that the UK R value is currently 0.9. In fact, the data shows that cases have started to rise again in those aged 20–39 but encouragingly, the case rate among those aged 60 and over have started to fall. The reasons behind the slowing of cases remains unclear but one theory proposed by the authors, is that after vaccination, people have become less guarded. Moreover, there is a large regional variation with the incidence of new cases. For example, the app data indicates that there are 16 to 26 new daily cases in London, but between 15 and 31 in Yorkshire and The Humber.

Nevertheless, the COVID symptom study, REACT-1 and the ONS data sources are in agreement, showing that that the infection rate in the UK is falling. but with case numbers still high, there is a need for caution and for maintenance of some mitigation strategies.

Citation
Data Press release. 19th February 2021. COVID Symptom study. https://covid.joinzoe.com/post/rapid-drop-in-cases-slows-down



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