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The government have published the latest estimates for the COVID-19 R number and growth rates.
Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:
“The Government have published their regular weekly revision to the ranges they provide for the R number and the growth (or decrease) rate of new infections. The range for R for the whole of the UK is 0.6 to 0.8 – lower at both ends than last week’s range of 0.7 to 0.9. That doesn’t mean that the R number itself has decreased – if it was 0.75 both weeks that would be in both ranges – but it’s likely that R has decreased. It’s pretty well certain that R is below 1, the level above which the number of infections will grow. As Professor John Edmunds pointed out in his comments for SMC last week, vaccination means that the number of infections won’t be related to pressures on hospitals, and to deaths, in the same ways that it has been up till recently. That’s certainly true. But not everyone can be vaccinated, and though there’s very good evidence that vaccinations can have a very strong effect on reducing serious illness and death even if someone is infected, the evidence about vaccination and things like long covid is not clear yet. So yes, we should probably stop obsessing about R, but we certainly shouldn’t forget about it entirely.
“The UK range for the growth rate of infections is now -7% to -4% a day. Negative growth rates are actually rates of decrease. A growth rate of -7% means that the number of new infections tomorrow will be 7% lower than the number today, and if that rate continues, it would mean that the number of new infections halved every 10 days. That’s a pretty fast rate of decline. A -4% growth rate would see infections halving about every two and a half weeks. Last week’s UK range was -5% to -3%, so the range has moved down this week, which means that new infections are probably falling faster that they were, on these estimates. This isn’t quite in tune with today’s results from the ONS infection survey, which gives some indication that infection numbers might be falling a little more slowly than the week before, but the difference isn’t huge. The R number and growth rate ranges from SAGE take into account a wide range of data, and some of it involves a delay (because of the time after infection that it can take for people to need hospital treatment, or to die, in unfortunately that happens), so small changes in trends won’t necessarily align across all the different estimates. In any case, the general pattern is still of reducing numbers of new infections.
“The Government ranges for R and the growth rate for England as a whole, and for the English regions, are encouraging too. The R and growth rate ranges for England are lower than they were last week. Some but not all of the regional R ranges are down compared to last week, and now none of them goes up as far as 1.0. (Last week one of them did.) At least one end of the growth rate range is lower this week than last in every region but one (the South East), and all of them indicate fairly rapid day-to-day decrease in new infections.
“This data release does not provide estimates of R and the growth rate for the devolved administrations, but it provides links to the latest estimates from the other UK countries, and all three of them are estimating that R is below 1 and the number of infections is falling rather than growing.”
All our previous output on this subject can be seen at this weblink:
www.sciencemediacentre.org/tag/covid-19
Declared interests
Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee. I am also a member of the Public Data Advisory Group, which provides expert advice to the Cabinet Office on aspects of public understanding of data during the pandemic. My quote above is in my capacity as an independent professional statistician.”