Why we are no longer focusing on the ‘R’ rate
THIS time last year all anyone was talking about was the “R” rate.
Getting “the R” below one was the single biggest stated aim of policy makers in Wales and the wider UK (as well as flattening the curve).
Now, however, nobody really seems to talk about it.
The R number represents the amount of people each person with Covid-19 is infecting with the virus.
If it goes above one the number of people becoming infected with the virus will grow exponentially, but for as long as it remains below one the number of people infected with the virus will continue to fall.
The latest figures suggest that Wales has a lower R rate than England but there are good reasons why no-one is really paying attention to the R rate at the moment.
How do Wales and England compare at the moment?
The latest published data from the Welsh Government’s Technical Advisory Cell, released on April 15, estimates the R rate in Wales to be between 0.6 and 0.9. These are the figures that come from Sage. However, other figures from Public Health Wales, which have less lag time and uses case data only, estimates with a high level of confidence that the R number is between 0.6 and 0.7.
By comparison information from England published on April 16 suggests the rate is between 0.7 and one.
An R value between 0.7 and 1.0 means that, on average, every 10 people infected will infect between seven and 10 other people.
By area in England it looks like this: ■ East of England - 0.7-1
■ London - 0.8-1.1
■ Midlands - 0.7-1
■ North east and Yorkshire - 0.7-1
■ North west - 0.6-0.9
■ South east - 0.6-0.9
■ South west - 0.7-1.1
Wales also has a lower R number than Scotland where the latest estimates published on April 8 put it as between 0.8 and one.
Why is this number not as important any more?
There are several reasons why the R number is no longer as important as it was.
■ Cases are low: The first is the fact that cases are currently low in Wales.
Though the rates of Covid are still fairly high in Wales’ cities, as we reported yesterday, the virus is reasonably suppressed in Wales now.
This means that the R rate is very volatile and just a few cases can cause it to sky rocket.
For example, if there is an outbreak in a meat processing factory like we saw last summer, the R rate could suddenly jump to three.
However, this would not mean that the virus is currently out of control in Wales. It is only when the R rate is high for a sustained period of time that it becomes a big issue when cases are this low.
■ The vaccines: This leads on to the second reason the R rate is not as important - hospitalisations.
The vaccines appear, for now, to have weakened the link between cases and people being admitted to hospital. The rates of Covid are significantly higher now than they were in the middle of the summer but hospital admissions are in fact lower.
This presents a new stage in the pandemic, where decision makers now have to balance the fact that the virus is not as deadly to vaccinated people and therefore more community transmission can be tolerated, with the fact that high transmission will still lead to some deaths and increases the likelihood of new variants that are resistant to the vaccines.
However, the fact that a big increase in cases no longer directly equals a big jump in deaths is a huge deal. This means that figures like hospitalisations are far more useful for assessing the state of the virus in Wales.
■ Slow data: Thirdly, the sheer sluggishness of the R rate to respond to what is happening on the ground makes it far from the most helpful metric.
The R rate figures quoted in this story are already several days old. In some cases they are well over a week old. Take the latest Wales advice. This advice was published on April 15 but was actually given to the Welsh Government on April 9. This means that a week has passed before the public are even aware of it. Even if we saw it on the 9th the data has still been subject to significant lag time.
Therefore as an instrument for assessing the current state of the pandemic it is not that useful at present.
When Wales came out of the firebreak in the autumn and cases started to spike again it took weeks until anything was reflected in the official R rate.