How quickly is the outbreak growing?

fullfact.org
6 min read
fairly difficult
Government scientists warned that new cases could double every week, which some people say is not realistic.
How quickly is the outbreak growing?

On Monday 21 September, the Chief Scientific Advisor, Sir Patrick Vallance, and the Chief Medical Officer, Professor Chris Whitty, gave a public briefing on Covid-19 in the UK.

During the briefing, Sir Patrick presented a chart showing the number of new cases reported each day up to 15 September, with an illustration of what would happen in future if the number doubled every week, which was their estimate of the current trend. Ultimately this would reach 49,000 new cases on 13 October. Sir Patrick said, "[the chart] is not a prediction, but it is a way of thinking about how quickly this can change."

However, some people have claimed that Sir Patrick's and Professor Whitty's illustration was not realistic. Professor Mark Woolhouse told the Science Media Centre that, "Many observers may consider this an implausible scenario. Presumably the UK government intends it to illustrate the consequences of sustained exponential growth."

The Conservative MP Lucy Allan said that the scientists "diminished their credibility with this sensationalist worst case scenario graph. Way out of quilter [sic] with other EU countries. Genuinely hope UK Govt Is not relying on this flawed data."

The broadcaster Andrew Neil said that the projection of about 50,000 cases a day by mid-October is not based on current trends. And on Sky News, Ed Conway said, "I'm not quite sure why the Chief Scientific Advisor is talking about doubling every seven days…" Mr Conway also expressed doubt over whether regular doubling would continue, citing case numbers from France and Spain. Articles on the BBC, Mail Online and unHerd websites made similar comparisons.

There are several estimates about how fast the epidemic is currently growing in the UK. Daily new cases doubling every week was one of the faster estimates that were publicly available on Monday. It is in line with data from the Covid Symptom app, a partnership between health science company ZOE and King's…
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