R number

It seems that Boris Johnson will not begin to think about lifting lockdown restrictions until we have clear evidence that the latest wave of the virus has almost been defeated. So it was not exactly good news yesterday from Imperial College’s React Covid survey, which suggested that even though we are in lockdown, the R number is still almost at 1 in Britain – meaning the epidemic is barely shrinking. As part of React’s ‘viral opinion poll’ swabs were taken from over 160,000 people in England between 6 and 22 January. And while the researchers rowed back on a claim in their previous report that active infections could be rising

As much as the government has any kind of strategy for lifting Britain out of lockdown it appears to revolve around the ‘R’ – or Reproduction – number. So long as this stays below one, we are told, the epidemic cannot progress – while the moment it strays above one then the disease will start to grow exponentially. That is easy enough to understand in itself. What is less easy to work out is just how this R number is calculated. We are told that for Britain as a whole it currently lies somewhere between 0.7 and 1. But whether this really means an awful lot is open to question.

Boris Johnson’s address on Sunday was always going to be challenging. The effects of Covid-19 – in terms of its horrific death toll and the drastic measures we’ve taken to prevent more loss of life – meant it was one the biggest and most important political statements in living memory. But what was also required was transparency and the explanation of very difficult scientific and medical concepts. In his statement, Boris Johnson drew attention to the R value, which he said was key to the changing lockdown measures over the coming weeks. If it crept above 1 this meant Covid-19 was spreading and the lockdown measures would remain in place, and