Official claim of 50,000 infections a day is based on just hundreds of cases

THE claim that Britain could face 50,000 Covid infections a day is based on studies that involve just a few hundred positive cases, it emerged yesterday.

Sir Patrick Vallance and Chris Whitty said in a dramatic televised statement on Monday that the disease rate could be doubling every seven days.

The chief scientific adviser and the chief medical officer said this might lead to 50,000 cases a day by the middle of next month. The projections sparked confusion because testing data showed it had taken a fortnight – not a week – for the total to climb from 2,000 a day to 4,000.

A former Cabinet minister said: ‘This tells us what everyone knew: that these two scientists are following groupthink which winds everything up so that they can’t be found guilty of doing the wrong thing. The Government should be calling this out.’

Hugh Pennington, an emeritus microbiologist at Aberdeen University, said of the graph that accompanied Monday’s projection: ‘It was almost designed to scare us. It certainly wasn’t a scientifically accurate model. It didn’t take into account we are doing a lot. I was annoyed because they were naughty doing that.’

Neither Spain nor France, which have been hit with a second wave ahead of the UK, are seeing rates doubling in a week. If Britain’s trajectory follows these two countries, there would be closer to 10,000 cases a day by next month.

A spokesman for Sir Patrick admitted that the ‘doubling in a week’ projection was based on a weekly survey by the Office for National Statistics and a similar less-frequent survey called React-1, run by Imperial College London. The studies both test a random sample of more than 100,000 people to track the progress of the virus. Because the virus is still at low levels, however, it involves making projections on the basis of small numbers of positive cases.

In its latest study the React-1 team sampled 153,000 people and found 136 cases, the last on September 7.

The Government said it used these surveys rather than actual testing data because it was concerned the testing data was lagging behind the spread of the disease.

Boris Johnson told MPs yesterday: ‘The chief medical officer and the chief scientific adviser warned the doubling rate for new cases could be between seven and 20 days, with the possibility of tens of thousands of new infections next month. Tens of thousands of daily infections in October would, as night follows day, lead to hundreds of daily deaths in November, and those numbers would continue to grow unless we act.’

Graham Medley of the London School of Hygiene and Tropical Medicine, who sits on the committee for the Government’s Scientific Advisory Group on Emergencies, Spi-M,

‘Accurate sense of the uncertainty’

said yesterday: ‘The estimates from Spi-M are ten to 20 days’ doubling time, but these are largely based on data from two to three weeks ago.

‘The concern was that the more recent doubling time is shorter. There was also concern that the problems with testing meant that the data were not particularly reliable.’

Steven Riley of Imperial College said having different sources of data was crucial.

‘The very well reported issues in the test and trace system mean that the proportion of infections that are picked up over time might not be constant,’ he said.

‘Studies like ONS and React are providing timely data, that is an alternative source to the test and trace data.

‘It’s not perfect, and when you’re estimating from 136 observations you have to make sure you give an accurate sense of the uncertainty.’