COVID-19 R Value And Growth Rates Published Showing Potential Growth In London

The government has today, Friday, June 19 published the UK wide and regional growth rates for England for the first time, alongside the R values.

According to the governments figures the current growth rate for the UK as a whole is between -4% to -2% while the estimated R value for the UK, as a whole, remains at 0.7-0.9.

The growth rate reflects how quickly the number of infections are changing day-by-day.

It is an approximation of the change of number infections each day and if the growth rate is greater than zero (+ positive), then the disease will grow, and if the growth rate is less than zero (- negative) then the disease will shrink.

The size of the growth rate indicates the speed of change, so a growth rate of +5% will grow faster than one with a growth rate of +1% and likewise, a disease with a growth rate of -4% will be shrinking faster than a disease with growth rate of -1%.

R value estimates do not tell us how quickly an epidemic is changing and different diseases with the same R can result in epidemics that grow at very different speeds.

For instance, a disease with R=2 with infection lasting years will grow much more slowly than a disease with R=2 with infection lasting days.

Growth rates provide us with different information to R estimates, by informing us of the size and speed of change, whereas R value only gives us information on the direction of change.

To calculate R, information on the time taken between each generation of infections is needed.

That is how long it takes for one set of people in an infected group to infect a new set of people in the next group, which can depend on several different biological, social, and behavioural factors.

The growth rate is estimated using a range of data similar to R, however it does not depend on the ‘generation time’ and so requires fewer assumptions to estimate.

Neither one measure, R nor growth rate, is better than the other but each provide information that is useful in monitoring the spread of a disease.

The R estimate and growth rates are not the only important measures of the epidemic and both should be considered alongside other measures of the spread of disease, such as the number of people currently infected.

As an average value, R can vary in different parts of the country, communities, and subsections of the population as it cannot be measured directly so there is always some uncertainty around its exact value.

RegionRGrowth rate % per day
England0.7-0.9-4 to -1
East of England0.7-0.9-6 to -1
London0.7-1.0-5 to +1
Midlands0.8-1.0-4 to 0
North East and Yorkshire0.7-0.9-5 to -2
North West0.7-1.0-4 to 0
South East0.7-0.9-5 to -1
South West0.6-0.9-6 to 0

Estimates of the growth rates and R are currently updated on a weekly basis.

However, as the numbers of cases decrease, these metrics will become less helpful indicators and other measures need to be considered, these include the number of new cases of the disease identified during a specified time period (incidence), and the proportion of the population with the disease at a given point in time (prevalence), and these will become more important to monitor.

Today the government also announced the lowering of the Alert Level from 4 to 3 while the number of cases increased by 1,346 to a total of 301,815 while the death toll increased by 173 to 42,461.