The Likely Progress of COVID-19 in the UK
Prof. John Ermisch
Leverhulme Centre for Demographic Science and Nuffield College
16 June 2020
email: john.ermisch [at] sociology.ox.ac.uk
Bottom line: expect 55,000 registered Covid-19 deaths by 29 June; the rate of increase in the UK’s confirmed cases remains high relative to other large European countries
This blog has been updated regularly for over 2 months, and so discussion of the details of the background analysis and methods used to forecast the likely progress of Covid-19 in terms of cases and deaths is relegated to the Analytical Appendix (see CLICK HERE above). The blog has forecast confirmed cases and deaths in the UK by relying on the development in cases and deaths in Italy, because it became clear by at least early April that the UK was about 2 weeks behind Italy in the pandemic but following a trajectory similar to Italy. As the progress of Covid-19 has slowed considerably, this is my last blog on the subject.
Deaths. The forecast of deaths in the UK assumes that the proportionate change in the UK during the 14 days following any particular base date is the same as that in Italy on the corresponding day since Italy’s lockdown. This procedure has been relatively accurate, as Figure 1 illustrates. For example, on 22 May it forecast the crossing (on 5 June) of the threshold of 40,000 deaths reported by Public Health England, and since 5 May the 14-day forecast error has been less than 2%. Average forecast errors from this procedure over the entire period of the blog are small (less than 300 deaths for the 14-day forecast).
Figure 1: 14-day ahead forecast of UK deaths and actual deaths
Death registration data up to 29 May suggest that the PHE figures for Covid-19 deaths in all settings understate the true number of registered Covid-19 deaths by at least 20%. Thus, a forecast of PHE-reported deaths by 29 June of 43,000 deaths suggests that we may expect a total of about 55,000 registered Covid-19 deaths by 29 June. Although understating the level of cumulative Covid-19 deaths, the PHE-reported deaths are a good indicator of changes over time in ‘excess deaths’ associated with the coronavirus: the correlation of cumulative excess deaths for each week and PHE deaths by the end of that week is 0.997.
Figure 2: Weekly Excess deaths and Covid-19 deaths during 2020, England and Wales
Excess mortality up to 5 June. The impact of the Covid-19 pandemic on mortality could be more, or less, than the number of deaths in which Covid-19 was mentioned on the death certificate. There are different ways to calculate ‘excess deaths’ corresponding to a disease. First, the timeframe of the calculation matters because deaths may be brought forward or postponed, say during a year, and so the excess deaths for the year is probably a more meaningful figure than the same calculation over a shorter time frame. Second, there must be a ‘counterfactual’; i.e. what would deaths have been had the disease been absent? Using death registration data up to 5 June for England and Wales, Figure 1 shows excess mortality for each of the first 23 weeks of 2020 using average deaths during the previous 5 years in the corresponding week as the counterfactual. It indicates negative excess deaths from mid-January to mid-March. After 13 March, excess deaths rose sharply, as did Covid-19 deaths, peaking in the week ending 17 April, during which registered deaths were 113% above average, and remaining high the following week (110% above average). Excess deaths fell sharply after 24 April, so that during the week ending 5 June excess deaths were only 7% above average and less than one-half of Covid-19 deaths during that week. It is possible that some of the excess deaths since 13 March are ‘deaths postponed’ from earlier in the year. For instance, during the pre-epidemic period up to 13 March, 65% of the shortfall in deaths relative to the 5-year average are accounted for by 3,200 fewer deaths from respiratory causes. Also, the peak of the epidemic in mid-April may have ‘brought deaths forward’. To take better account of such intertemporal substitution we measure excess deaths as deaths during the first 23 weeks of 2020 above the 5-year average for these weeks. On this accounting, excess deaths in England and Wales were 53,870, or 21% above average. Covid-19 deaths during the same period were 47,100. Thus, in addition to the Covid-19 deaths during the first 23 week there were another 6,770 deaths above average, some of which may be misdiagnosed Covid-19 deaths. If we had only looked at the period since 13 March, as many newspapers report, we would obtain 58,770 excess deaths, or 49% above average for those weeks.
Confirmed cases. As the pandemic proceeded, the usefulness of the forecasting approach for confirmed cases sketched above became more doubtful because the UK has diverged from Italy during the recent progress of the pandemic, as illustrated in Figure 3. UK’s proportionate rate of increase in confirmed cases has come down in recent days, but at about 0.5% per day (about 1,400 cases per day) it remains well above that in Italy, Spain and Germany, for which it is less than 0.2% per day, and 0.3% per day in France. All the countries in Figure 3 had begun easing their lockdown by at least 13 May. The UK enters its latest phase of lowering restrictions (on 15 June) with a new infection rate persistently higher than its European neighbours, and so with respect to Covid-19, it is the sick man of Europe.
Figure 3: Daily proportionate increase in confirmed cases since beginning of May, 7-day moving average