A Public Health leadership statement from:
- Cabinet member for Public Health, Cllr Maureen McLaughlin
- Director of Public Health for Warrington Borough Council, Eileen O’Meara
You may have seen recently published figures reporting ‘R values’ for COVID-19 at a council/ local authority level. It is important to understand that R values on a local level are not wholly reliable.
The R value is the reproduction number of the virus – this means the average number of people who are infected by one person who has COVID-19. R is calculated using a range of coronavirus-related data, such as the number of confirmed cases, the number of people hospitalised from the virus and the number of COVID-related deaths.
It is a complex, statistical calculation and can generally only be reliably interpreted for large populations. For smaller populations (such as Warrington, for example) the range that we can confidently say R falls between is generally quite large. Even at a national level, experts can only be confident in saying that the range is currently between 0.7 and 0.9. This means R, as a measure, is less useful to us at a local authority level in assessing the local picture in relation to current risk from coronavirus.
R will also change over time due to changes in our behaviour. For example, lockdown and people having less contact with others has brought R down substantially, from between 3 and 4 nationally at the start of the pandemic to between 0.7 and 0.9 now.
The calculated R value may also alter because of a change in the underlying data that is included in the calculation, and this may skew what is actually happening in the community. For example, because there has been an increase in availability of testing for the general population, more cases may be detected. This will impact on R simply because we know about more cases, not because there are more cases.
For all of these reasons, scientific and medical experts do not advise that we use R at a local authority level, as it may be misleading and even potentially dangerous if it provides false reassurance, or creates unnecessary concern.
Instead, within Warrington, we keep a close eye on the regional values for R, which are published by leading academics and experts at Public Health England and the University of Cambridge and the London School of Hygiene and Tropical Medicine.
We also closely monitor the local data that we know we can be more certain about: the number and trend in hospital admissions for COVID-19 and, sadly, deaths from COVID-19. Our daily monitoring includes a review of:
- Data on confirmed cases from Public Health England
- Data on individuals in hospital who have tested positive (this data is not public)
- Data on outbreaks in community settings (this data is not public)
- Data on the number of COVID-19 deaths according to the Office for National Statistics
Overall, to date, the rate of diagnosed cases in Warrington has been higher than the national average. This is likely to be due, at least in part, to the increased availability of testing in place locally in the early weeks of the pandemic compared to other areas and regions.
The trend in the number of cases shows a steady decrease. The trend in Warrington residents hospitalised as a result of coronavirus has also decreased substantially. At the peak of the pandemic in early April there were, on average, 10 new COVID-19 admissions per day. The latest data shows that this has reduced to an average of two per day.
We also know that the number of deaths from coronavirus has also reduced substantially. During the peak week (mid-April for deaths) 41 Warrington residents sadly died with COVID-19. The latest week for which we have validated data (week ending 29 May) shows that the number of people taken by coronavirus had reduced to six in that week.
As a council, we are working with our local NHS colleagues and partners in Public Health England to ensure that we continue to respond to the pandemic in a safe and effective way. We, of course, all have a part to play and it is essential that we continue to follow the national guidance.