NIESR Weekly Covid-19 Tracker: Reproduction Number (R) and Forecasts of New Cases: Local surges and flare ups

Publication date: 20 May 2021 | Publication type: NIESR Covid-19 Tracker | NIESR Author(s): Thamotheram, C Issue 14

Main points

  • We report estimates of the R number and forecasts for new cases of Covid-19, hospital admissions, and deaths due to Covid-19 using data that was publicly available as of 18th May 2021.
  • Figure 1 shows that the Reproduction number, R, for England. R is the average number of secondary infections currently generated by an infected individual, and is estimated to be in the range of 0.90 – 1.05 based on specimen date data until 14th May.
  • This is to be seen in the context of 7-day case rates (calculated as the count of cases per 100,000 people over the last 7 days) in all nations and regions being less than 50 per 100,000 people. From this low base small changes in case numbers can have large effects on growth rates of new cases. As R is calculated directly as a function of growth rates of new cases (see Harvey and Kattuman, 2020b) the Reproduction number, R, if considered in isolation, can give a misleading picture.
  • For Northern Ireland the R number is in the range 0.85 – 1.00 (7-day case rate per 100, 000 of 35); for Wales, 0.95 – 1.10 (case rate of 10) and for Scotland, 1.15 – 1.30 (case rate of 35). The regional R number estimates and case rates given in Figure 5 show that, currently, the South West (case rate of 9) has the lowest R number while the North West (case rate of 37) has the highest value across England’s regions.
  • With this edition of the tracker we begin monitoring local authorities with relatively high case rates, resulting from flare ups which have the potential to seed a new wave. Figure 6 shows that the R number is in the range 1.20 - 1.55 for Bolton (case rate 302), 1.15 - 1.55 for Blackburn and Darwen (case rate 132) and 1.00 – 1.50 for Bedford (case rate 128).
  • Based on our model, by 21st June when step 4 re-opening is due, we expect the trend value of daily cases in the UK to be around 1,200; admissions to be below 100, and deaths to be well below 25 (Figures 3-5).


“It is reassuring that the weekly case rate per 100,000 is smaller than 50 in all regions and nations. However, evident localised outbreaks have the potential to seed a new wave. The extent to which these flare ups are contained will be key in the weeks ahead. Based on the latest data on new cases, our estimate of the R number for England lies in the range 0.90 – 1.05, decreasing from last week. This estimate is based on data up to 18th May 2021, just at the start of step 3 re-opening. Hospital admissions and deaths due to Covid-19 continue their steady decline.”

Dr Craig Thamotheram
Senior Economist - Macroeconomic Modelling and Forecasting


Please find the full analysis in the document attached