Ross Clark Ross Clark

The mystery over Covid infection numbers

(Photo by JANE BARLOW/POOL/AFP via Getty Images)

This morning’s so-called ‘React study’ — an attempt by Imperial College to estimate the prevalence of current Covid-19 infection in Britain — has aroused much interest thanks to its suggestion of a sharp fall in the R number. Its central estimate for R is 1.06, but it applies a range of between 0.74 to 1.46, with a 63 per cent chance that R is above the critical level of 1. 

It was a rare piece of good news to lead BBC news bulletins — as well it might given that it was the previous report from the React study three weeks ago that led to the government introducing the rule of six.

It underlines just how unreliable much of the data on Covid-19 still is

But there are a couple of interesting details about the React study that have gone unreported. Firstly, its estimate of the number of people in England who are currently infected with Covid-19 is vastly higher than is suggested by official figures for confirmed cases. React, which tests swabs from a randomised sample of the population, estimates that between 351,000 and 478,000 people in England are currently infected, with a central estimate of 411,000. 

Over the past fortnight, by contrast, 61,617 people have officially been diagnosed as having the virus. Even since the beginning of the crisis only 388,342 people have officially tested positive (the vast majority of whom tested positive more than a fortnight ago and should not still be carrying the virus). If the React estimate is anything close to reality, it suggests that the vast majority of infections are being missed, in spite of the huge increase in testing. If the government is only succeeding in catching a small percentage of cases there is zero possibility of controlling the virus through test and trace.

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