Press Release: NIESR Weekly Covid-19 Tracker – Reproduction Number (R) and Forecasts of New Cases: New cases still decreasing but R number on the rise

Post Date
25 March, 2021
Reading Time
3 min read

Main points

  • We produce timely estimates of the R number and report forecasts for new cases of Covid-19, hospital admissions and deaths due to Covid-19 using publicly available data on 23rd March 2021.
  • Following government definitions data on cases can be represented by specimen date or by published date. Specimen cases refer to cases by the date when the sample was taken from the person being tested and published cases refer to cases by the first date when they are included in the published numbers. At the present time we regard the specimen date data as a more reliable indicator of the trend in new cases as the model based on specimen dated observations has better captured the sharp increase in testing on the day that schools reopened.
  • Figure 1 shows that the Reproduction number, R, which is the average number of secondary infections currently generated by an infected individual, estimated using the specimen date data, had moved up to 0.9 – 1.0 by 19th March which is again higher than SAGE’s estimates. This estimate was obtained after controlling for enhanced testing in schools that started when they reopened on the 8th of March. If enhanced testing in schools is not controlled for, the R estimate would be in the range 0.9 – 1.05.
  • Based on our model, by 12th April when non-essential retail is scheduled to reopen, we expect the trend value of daily cases to be around 3,800; admissions to be around 100, and deaths to stay below 50 (Figures 3-5). Our forecasts for admissions and deaths are unchanged relative to last week, but our forecast for cases is higher by 900. If enhanced testing in schools is not controlled for, the number of cases would be 4,300.
  • To the extent that each stage of re-opening increases transmission these numbers may increase. At the same time, expansion of the vaccination programme can be expected to reduce transmission. The trajectory that nets out these opposing trends will become evident in the weeks to come.
  • Figure 5 shows that regional R number estimates have increased. Currently, the London has the lowest R number while Yorkshire and the Humber has the highest


Dr Craig Thamotheram, Senior Economist – Macroeconomic Modelling and Forecasting, said:“Based on the latest data on new cases, our estimate of the R number for the UK lies in the range 0.9 – 1.0, taking it above the range it was last week. This estimate is based on data up to 23rd March 2021, just over 2 weeks after the schools were reopened on the 8th of March. After controlling for increased testing in schools our model indicates that increased transmissions are pushing the estimate of the R number ever closer to 1 at which point daily cases would again start to rise. Reassuringly, hospital admissions and deaths due to Covid-19 continue their steady decline.”


Please find the full analysis in the document attached


Notes for editors:

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Luca Pieri on l.pieri [at] / 07930 544 631

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