R Drops Before Easter

Pub. Date
08 April, 2021
Pub. Type

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 on 6th April 2021.
  • Data on Covid-19 cases are reported by the government by ‘specimen date’ and by ‘published date’. Specimen cases relate to the date when the sample was taken from the person being tested, while published cases relate to 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. The model based on specimen dated observations has better captured the effect of 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 until 2nd April, decreased to 0.75 – 0.85. For specimen cases, we choose to set the Easter bank holidays to missing values to downplay the under reporting on bank holidays that was observed on previous bank holidays. We leave published cases unchanged.
  • Further evidence from Imperial’s REal-time Assessment of Community Transmission-1 (REACT-1) confirms the levelling off in cases we reported in mid to late March. Their study based on home swab tests conducted between 11th to 30th March and released on 8th April estimated the R number at 1.0 during this period. This again highlights the timeliness of our method for estimating the R number – our estimates were in that range some 2 to 3 weeks before the REACT-1 estimates were published.
  • 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 1,900; admissions to be around 100, and deaths to stay well below 50 (Figures 3-5). Our forecasts for deaths are unchanged relative to last week, but our forecast for admissions is lower by 100 and cases by 1,900.
  • 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 6 shows the regional R number estimates. Currently, the South West has the lowest R number while the North East has the highest.

“Based on the latest data on new cases, our estimate of the R number for the UK lies in the range 0.75 – 0.85, down from just below 1 last week. This estimate is based on data up to 6th April 2021. Our R number estimate sat just below 1 from mid to late March. This is above those of SAGE but now supported by the survey estimates from the REACT-1 study of Imperial College published on 8th April. Reassuringly, data in the week before the Easter break shows a consistent decrease in cases. This has pushed our R estimate down. Hospital admissions and deaths due to Covid-19 continue their steady decline.”