An enormous amount of radio, television and print coverage has been devoted to the coronavirus pandemic, often accompanied by misleading and alarmist graphics culled from the raw data provided by the UK Coronavirus Dashboard and other sources. Without in any way wishing to question the severity of the epidemic in the UK, I believe that it is possible to present a more realistic view of the actual situation to date.
Chart 1 summarises key metrics downloaded from the UK coronavirus Dashboard. Practical considerations mean that some of the values, in particular the daily number of hospital admissions, reported on the daily Dashboard are provisional and subject to revision over time. More stable data is available from the download section of the Dashboard a week or so later. In Chart 1 the weekly values have been scaled by Z-score normalisation (whereby the mean of each data series, Mean[D], is subtracted from each value in that series, d, the result being divided by the standard deviation of the series StdDev[D]). As can be seen most values fall within two standard deviations of the mean. The chart and discussion will be updated regularly during the course of the pandemic.
Z-Score Standardised UK Weekly Data reported for the weeks ending 29th February 2020 to 27th February 2021
Data Series Chart Symbols Weekly data series description Weekly Minimum Weekly Maximum Virus Tests Conducted [dotted blue line] Number of PCR and Lateral Flow tests processed. 67,469 [ 04 Apr 20 ] 4,414,120 [ 06 Feb 21 ] Confirmed Cases [dotted red line] Number of positive tests reported. 183 [ 07 Mar 20 ] 417,620 [ 09 Jan 21 ] % of Positive Tests [solid red line] Percentage of the tests reported as positive. 0.5% [ 18 Jul 20 ] 38.8% [ 04 Apr 20 ] Hospital Admissions [solid yellow line] Number of patients admitted to hospital 693 [ 22 Aug 20 ] 28,717 [ 16 Jan 21 ] Deaths [solid black line] Number of deaths within 28 days of a positive test 2 [ 07 Mar 20 ] 8,739 [ 23 Jan 21 ] R [see note] [smoothed green line] The ratio of the percentage of positive tests adjusted for the
number of tests per week in successive weeks
- Coronavirus testing and hospital admission data are not available for March 2020.
- Patient hospital admissions are generally reported a few days later than the rest of the data.
- The reproduction number R, which is an approximation, has not been standardised.
Testing and the number of confirmed cases
The number of people testing positive each week [dotted red line] surged in September and October and again very rapidly in December 2020 and January 2021. However, this does not take into account the number of PCR [polymerase chain reaction] and Lateral Flow tests conducted [dotted blue line], which increased from around 110,000 per week in early April to about three million per week by late-December. The percentage of positive tests [solid red line] is a much better metric, assuming that those tested are a consistently representative sample of the overall population. While this assumption is not necessarily robust, the standardised data do follow a consistent pattern.
Hospital admissions and deaths
During the first wave of coronavirus infections the weekly percentage of positive tests and the number of hospital admissions peaked in mid-April 2020, followed by a peak in deaths a couple of weeks later. A similar but less alarming trend which developed in October was somewhat mitigated by the four-week lockdown ending on 2nd December. Then the number of infections, hospital admissions and Covid-related deaths soared and it was clear that the more infectious variant of Covid was getting out of control. The proportion of deaths to hospital admissions, which fell during the summer, is now at a similar level to April 2020.
Reproduction number R
For the purposes of this summary the reproduction number, R, the average number of secondary infections produced by a single infected person, has been estimated as the ratio of the percentage of positive tests adjusted by the overall number of tests in successive weeks. R is plotted as a smoothed solid green line on the chart. Note that this value may 'bounce around', with the ratio changing noticeably from week to week, particularly when the number of cases nationally is low. The general trend over a month or so is more meaningful. Thus the first lockdown in March resulted in a decrease in R, followed by a slow increase during the summer, when infections were low. In September the general trend was a more rapid rise, followed by a slow decline during the November lockdown and a more rapid rise in the run up to Christmas. The effects of the January 2021 lockdown and the vaccination campaign can now be seen.
Overall number of infections
The Imperial College REACT immunoassay study of 109,000 randomly selected participants in England conducted between 20th June and 13th July estimated that around 3.3 million people, approximately 6% of the population of England, had antibodies to SARS-CoV-2 by the end of June 2020, the overall infection fatality ratio being 0.90%. The proportion of the population who have contracted the virus is now significantly higher, probably by a factor of three or more. Recent modelling reported in The Guardian [11th January 2021] suggested that over 12 million people in England may have been infected by that date.
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© Chris Newall 2021
Author : Chris Newall
Page created on : 12th October 2020
Last updated on : 1st March 2021