A Whitehall source confirmed that preparations to incorporate “backward”, or retrospective, contact tracing into the current system were under way. “That is our plan,” the source said. “We just can’t do it while prevalence is as high as it is now.”
Backward contact tracing works on the principle that tracking the person who infected a Covid-positive patient, rather than just the subsequent contacts of that patient, could allow officials to find “super-spreader events” at which one individual has been responsible for as many as thousands of infections.
Having traced the person who transmitted the virus to the Covid-positive patient, officials would then seek to find others infected by the same person.
South Korean officials have traced more than 5,000 cases back to one woman who attended a service at a mega-church in the country.
Addressing MPs in July, Prof Whitty said: “Backward contact tracing is, we think, an increasingly important thing to do … One thing that is now much clearer, but was not clear at the beginning of the epidemic, is that the disease is passed on in clusters. The Koreans and the Chinese have demonstrated that really well.
“You might have a situation where the great majority of the transmission comes from about 20 per cent of the people who get it, and the rest do not transmit very much; and it is a particular environment.
“Backward contact tracing to find those environments and go back to find who has been to those environments is something we should be aiming to do – and the lower the transmission rate, the easier it is.”