The ‘R’ value refers to the number of people who can expect to catch the virus from an infected person. If it is greater than one, the infection will spread exponentially, but if it is lower then it will spread slowly and eventually die out.
Earlier this week, Dominic Raab, the Foreign Secretary, said the ‘R’ rate stood at between 0.5 and 0.9, although it was estimated to be between three and 4.6 in parts of Europe at the start of April before lockdowns came into effect.
Last week Boris Johnson, the Prime Minister, said “driving down the ‘R'” was the country’s “collective endeavour”.
Sir Ian said there was some variation across the UK, which is why it was safer to give a range, and added: “Clearly there is some variation, and we are absolutely working with some fantastic estimates that are done by our modelling community.
“And I think the consensus is that it is below one everywhere, lowest probably in London, but certainly some variation across the different regions.”
Sir Ian was commenting on new estimates from Prof Edmunds, a professor of infectious disease modelling at the London School of Hygiene and Tropical Medicine.
Prof Edmunds told MPs that, a couple of weeks ago, he would have said the ‘R’ was at 0.6 or 0.7, possibly up to 0.8, but because of infection rates in care homes and hospitals the overall estimate stood at up to one.
He said: “It’s a big problem that we have in hospitals and care homes, but I think what’s happened is that the community epidemic has come down and that epidemic is now being concentrated in these settings.
“Our data are really not really good enough to give us any certainty about what the reproduction number really is in hospitals. It’s probably variable between one hospital and another, and care homes is even worse.
“The epidemic in the community has shrunk really considerably over the last five or six weeks – the lockdown has worked in that regard – but what we’re seeing is this continuing epidemic in hospitals and care homes.
“So what we’re now measuring as a reproduction number is a measure… to a large extent is this residual transmission in these settings [care homes].”
He also said the data could not show whether poor practice in care homes was driving up the ‘R’ rate.
Prof Edmunds, who sits on the Scientific Advisory Group for Emergencies (Sage), which advises ministers, estimated that there are currently around 20,000 new virus cases a day.
He said: “The incidence has to come right down for contact tracing to be feasible really, to be able to contact trace all of those contacts for those individual cases. I do think that we will need other social distancing measures in place.”
Mr Johnson told MPs at Prime Minister’s Questions on Wednesday that he “bitterly regrets” the coronavirus crisis in care homes and insisted the Government was “working very hard” to tackle it.