Coronavirus infections in hospitals and care homes are spilling into the community and sustaining the outbreak to the point that cases will remain steady until September, a leading scientist has warned.
Prof Neil Ferguson, the head of the outbreak modelling group at Imperial College London, said he was shocked at how poorly care homes had been protected from the virus and that infections in UK care homes and hospitals were now feeding into the epidemic in the wider community.
R, or the 'effective reproduction number', is a way of rating a disease’s ability to spread. It’s the average number of people on to whom one infected person will pass the virus. For an R of anything above 1, an epidemic will grow exponentially. Anything below 1 and an outbreak will fizzle out – eventually.
At the start of the coronavirus pandemic, the estimated R for coronavirus was between 2 and 3 – higher than the value for seasonal flu, but lower than for measles. That means each person would pass it on to between two and three people on average, before either recovering or dying, and each of those people would pass it on to a further two to three others, causing the total number of cases to snowball over time.
The reproduction number is not fixed, though. It depends on the biology of the virus; people's behaviour, such as social distancing; and a population’s immunity. A country may see regional variations in its R number, depending on local factors like population density and transport patterns.
Hannah Devlin Science correspondent
Ferguson, who quit as a member of the government’s Scientific Advisory Group on Emergencies (Sage) after breaking social-distancing rules, said that infected staff carrying the virus out of the workplace explained why the R value, the average number of people infected by a case, remained only marginally below one.
“I, like many people, am shocked about how badly European – or countries around the world – have protected care home populations,” Ferguson told a hearing of the Lords science committee. About 16,000 UK care home residents are believed to have died from Covid-19 in outbreaks that have struck 38% of care homes in England and 59% in Scotland.
“The infections in care homes and hospitals spill back into the community, more commonly through people who work in those institutions. If you can drive the infection rates low in those institutional settings, you drive the infection low in the community as a whole,” Ferguson said.
With the virus still circulating widely and restrictions being eased, Ferguson said there was “limited room for manoeuvre.” Lockdown reduced the spread of infection by about 80%, he said, “but to maintain control, we need to keep that transmission suppressed by about 65% so we have a little bit of wriggle room.”
Prof Matt Keeling from Warwick University, whose modelling group is now providing the government’s “worst case scenario”, suggested that researchers might have done more to understand the risks to care homes in particular.
“If the lockdown had been very strict, if we’d have thought more about what was happening in care homes and hospitals early on, maybe that was one of the areas where modellers did drop the ball,” Keeling told the hearing. “With hindsight, it’s very easy to say we know care homes and hospitals are these huge collections of very vulnerable individuals, so maybe with hindsight we could have modelled those early on and thought about the impacts there.”
The researchers said it is still unclear what impact the recent easing of restrictions will have on the spread of the virus, but Ferguson dampened any expectations that the epidemic might peter out any time soon. “I suspect that under any scenario, the level of transmission and number of cases will remain relatively flat between now and September, short of very big policy changes or behaviour changes in the community,” he said.
“The real uncertainty is if there are larger policy changes in September, as we move into the time of year when respiratory viruses tend to transmit slightly better, what will happen then? And that remains very unclear,” he added.
Under further questioning about the outbreak, Ferguson described how scientists realised in early March that the UK had been much more heavily infected than anticipated, and that this was one of the reasons the country now has if not the largest, then one of the largest, epidemics in Europe.
“One thing the genetic data is showing us now is most chains of transmission still existing in the UK originated from Spain, to some extent Italy,” Ferguson said. “It is clear that before we were even in a position to measure it, before surveillance systems were even set up, there were many hundreds, if not thousands, of individuals coming into the country in late February and early March from that area. And that meant that the epidemic was further ahead than we had anticipated.”
“That explains some of the acceleration of policy then. It also explains, to some extent, why mortality figures ended up being higher than we had hoped,” he added.
As ministers ease restrictions in England, health officials will rely on the new test-and-trace system to identify and clamp down on new outbreaks. The tests would be offered to people with symptoms, but since many people were infectious before feeling ill, and many never show symptoms at all, the system would have only limited use, the committee heard.
“By the time someone shows symptoms they have probably been infectious for a day or two,” said Adam Kucharski, an associate professor and infectious disease modeller at the London School of Hygiene and Tropical Medicine. “As soon as someone becomes symptomatic, you have a very short time window before their contacts may become infectious and then you’ve got another generation of transmission to deal with.”
Ferguson said the test-and-trace scheme “was not a panacea” because it relied not only on what proportion of people developed symptoms, but what proportion could identify past contacts, how quickly they could be contacted, and how many then abided by the self-isolation rules. He told the hearing that if the system worked perfectly, it might at best reduce R by 0.2 to 0.25, describing that as “significant, but not huge”.
