Virus growth rate ‘may be increasing’
THE growth rate and R value of coronavirus transmission in the UK has changed slightly since last week – with early indications the value may be increasing.
Figures published yesterday by the Government Office for Science and the Scientific Advisory Group for Emergencies (Sage) revealed the growth rate to be between minus 5% to 0, slightly up from between minus 4% to minus 1% last week.
The reproduction number, referred to as R, for the UK as a whole is between 0.8 to 1.
In England, the R is between 0.8 and 1, but Sage has indicated it is not confident that R is currently below one in the region.
The R value also appears to be close to 1 in all the other regions. The estimates for R and growth rate are provided by the Scientific Pandemic Influenza Group on Modelling (SPI-M), a subgroup of Sage.
It said: “We are starting to see early indications that these values may be increasing. This is not yet reflected in these estimates because the data used to calculate R and growth rate reflect the situation from a few weeks ago.”
A time delay between initial infection and the need for hospital care usually means it may take between two to three weeks for the changes in the spread of Covid-19 to be reflected in the estimates.
But models that use Covid-19 testing data, which have less of a time delay, indicate higher values for R in England, the Government Office for Science statement said.
It added: “For this reason, Sage does not have confidence that R is currently below one in England.
“We would expect to see this change in transmission reflected in the R and growth rate published over the next few weeks.”
However, the Government officials and advisers said is also important to recognise that these are estimates, and there is a high degree of uncertainty with them. The growth rate reflects how quickly the number of infections is changing day by day and, as the number of infections decreases, it is a way of keeping track of the virus.
If it is greater than zero, and therefore positive, then the disease will grow, and if the growth rate is less than zero, then the disease will shrink. The R number represents the number of people each Covid-19 positive person goes on to infect.
In London, the growth rate is between minus 4% and plus 1%, compared with minus 4% and 0 last week. The capital has an R value of 0.8-1.1. Across England, the growth rate is between minus 3% and 0, compared with between minus 4% and minus 1% last week.
Meanwhile, statisticians at the Medical Research Council Biostatistics Unit at the University of Cambridge, which feeds information directly to the SPI-M, said on Thursday the R value was now likely to be close to 1 in most regions, with the South West potentially above 1, although the low number of overall infections makes it difficult to be accurate about the spread of the disease.