Guidance: The R value and growth rate

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State of the UK epidemic

To better understand the state of the epidemic in the UK, we recommend focusing on indicators for the 4 nations of the UK individually, rather than an average value across the UK.

Estimates of the R value and growth rate for England and NHS regions are given below.

The latest ranges for R values and growth rates in the devolved administrations are published on their respective websites:

UK estimates of R and growth rate are averages over different epidemiological situations and should be regarded as a guide to the general trend rather than a description of the epidemic state.

Given the increasingly localised approach to managing the epidemic, particularly between nations, UK-level estimates are less meaningful than previously and may not accurately reflect the current picture of the epidemic.

The R value and growth rates for the 4 nations and NHS England regions are more robust and useful metrics than those for the whole UK. As a result, UK estimates of the R value and growth rate will no longer be produced.

Latest R and growth rate for England

An R value between 0.8 and 1.1 means that, on average, every 10 people infected will infect between 8 and 11 other people.

A growth rate of between -4% and -1% means that the number of new infections is shrinking by between 1% and 4% every day.

These estimates represent the transmission of COVID-19 2 to 3 weeks ago, due to the time delay between someone being infected, developing symptoms, and needing healthcare.

R estimates now span 1 for England and some NHS England regions. This does not necessarily mean R is definitively above 1 and that the epidemic is increasing, just that the uncertainty means it cannot be ruled out.

Latest by NHS England regions

These are the latest R and growth rate estimates by NHS England regions.

Region R Growth rate % per day
England 0.8 to 1.1 -4 to -1
East of England 0.8 to 1.1 -4 to 1
London 0.8 to 1.1 -5 to 0
Midlands 0.7 to 1.0 -4 to -1
North East and Yorkshire 0.8 to 1.0 -7 to -2
North West 0.7 to 0.9 -6 to -2
South East 0.8 to 1.0 -4 to 0
South West 0.8 to 1.2 -4 to 1

When the numbers of cases, hospital admissions or deaths are at low levels and/or there is a high degree of variability in transmission across a region, then care should be taken when interpreting estimates of R and the growth rate. For example, a significant amount of variability across a region due to a local outbreak may mean that a single average value does not accurately reflect the way infections are changing throughout that region.

Until 28 April, daily deaths in a region averaged over a 10-day period have been used when calculating an estimates reliability score, to determine whether it is based on very few cases in a particular area. These data were agreed to be the most reliable data stream when the indicator was developed in summer 2020. Over recent months, the number of deaths has been driven down to very low levels due to lockdown and the impact of the COVID-19 vaccination programme, consequently reducing reliability scores for many regions. As a result, the number of individuals admitted to hospital with COVID-19 and inpatients newly diagnosed with COVID-19 will now replace deaths as an indicator for whether the estimate is based on very few cases in a region.

Estimates for R and growth rates are shown as a range, and the true values are likely to lie within this range. The estimate intervals for R and growth rate may not exactly correspond to each other due to the submission of different independent estimates and rounding in presentation.

See a time series of published R and growth rate estimates (ODS, 24.4KB) for:

  • England
  • the 7 NHS England regions

Historical UK estimates up to 26 March 2021 are also included. The time series document is updated regularly.

Other key statistics

The ONS Infection Survey provides information on:

  • the number of new infections of the disease identified during a specified time period (incidence)
  • the proportion of the population that test positive for the disease in the community at any given point in time (positivity rate or prevalence)

Other data on testing, cases, healthcare, vaccinations and deaths is available at the Coronavirus (COVID-19) in the UK dashboard.

About R and growth rate

R

The reproduction number (R) is the average number of secondary infections produced by a single infected person.

An R value of 1 means that on average every person who is infected will infect 1 other person, meaning the total number of infections is stable. If R is 2, on average, each infected person infects 2 more people. If R is 0.5 then on average for each 2 infected people, there will be only 1 new infection. If R is greater than 1 the epidemic is growing, if R is less than 1 the epidemic is shrinking. The higher R is above 1, the more people 1 infected person infects and so the faster the epidemic grows.

R can change over time. For example, it falls when there is a reduction in the number of contacts between people, which reduces transmission. R increases when the numbers of contacts between people rise, leading to a rise in viral transmission.

Growth rate

The growth rate reflects how quickly the numbers of infections are changing day by day. It is an approximation of the percentage change in the number of infections each day. If the growth rate is greater than 0 (+ positive), then the epidemic is growing. If the growth rate is less than 0 (- negative) then the epidemic is shrinking.

The size of the growth rate indicates the speed of change. A growth rate of +5% indicates the epi



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