The UK’s coronavirus reproduction number, or R rate, is estimated to have fallen slightly to between 0.7 and 1.0, according to government figures.
Last week, it was between 0.7 and 1.1. It is the fifth week in a row the R rate has dropped.
R measures the number of people, on average, that each sick person will infect.
If R is greater than 1 the epidemic is generally seen to be growing; if R is less than 1 the epidemic is shrinking.
The R number, explained
The R number – sometimes referred to as the R0 – is the “basic reproduction number”. It’s used to measure the transmission potential of a disease.
The R value represents the number of people that one infected person will, on average, pass the virus on to. It’s influenced by characteristics of the specific disease (in this case, Covid-19), such as how easily it passes from person to person. Human behaviour – i.e. how closely we follow social distancing measures – will also impact the R number.
When the R number is below 1, this suggests the number of cases is shrinking. Anything above 1 suggests cases and subsequent infections are growing – and is a cause for concern, because cases snowball.
An R rate of 0.7 and 1.0 means every seven people infected will on average infect eight to 10 others between them.
While it can help indicate if lockdown measures are working, the R number doesn’t offer the full picture; the R value can show if an epidemic is getting bigger or smaller, but not how large it is.
“R should always be considered alongside the number of people currently infected,” the government website explains. “If R equals 1 with 100,000 people currently infected, it is a very different situation to R equals 1 with 1,000 people currently infected.”