‘Social bubble’ could be limited to fewer than 10 friends and family

Models for restarting work and school recommend restrictions on meeting to control virus reproduction

SOCIAL contacts outside home, work and school may have to be limited to less than five a day even if widespread coronavirus testing and contact tracing is introduced as part of an exit strategy.

New modelling shows the scope for loosening lockdown measures is extremely limited if the reproduction number of the virus (R) is to be kept under one and a second peak avoided.

Two separate studies published last week by British academics draw the same basic conclusion: R can only be kept below one if the number of social contacts people have outside their homes remains tightly constrained until a vaccine becomes available. Both are likely to be being pored over this weekend by the Scientific Advisory Group for Emergencies (Sage), which will report to ministers next week.

A study by The Centre for the Mathematical Modelling of Infectious Diseases (CMMID) at the London School of Hygiene & Tropical Medicine found that under “optimistic” assumptions, contacts may have to be kept at less than 5-10 a day outside home, work and school if a contact tracing strategy of the sort Britain has capacity for were pursued.

A second study by the Division of Molecular and Clinical Medicine at the University of Dundee found that if the public resumed more than 10 per cent of their previous contacts, the country would risk a second peak of the virus. “Lockdown can barely contain the disease’s spread,” say the authors. “Discussions around exit strategy need to move on from optimistic concepts of returning rapidly to normal activity. Our data is more consistent with a need to adopting a “new normal” that can provide the optimal balance between allowing economic activity while ensuring very substantial reductions in prior social contacts – 90 per cent reductions according to our estimates”.

Adam Kucharski, lead author of the CMMID study, told The Sunday Tele

graph the key to keeping R under one was to stop the virus spreading between households. “It’s going to be very hard to maintain control of the virus without some form of physical distancing unless your contact tracing is getting people isolated and tested really quickly, and getting to their contacts really quickly,” he said.

Mr Kucharski and his co-authors used a database of social interactions gathered by the BBC as part of a social experiment which ran to coincide with the centenary of the 1918 Spanish flu pandemic to model different exit strategies. The data was collected between September and November 2017 via a mobile phone application which simulated the spread of a highly infectious virus across the UK and involved tracking 40,162 participants. A social contact was defined as having taken place where there was a “conversation or physical touch”.

Although the study suggests a limit of four social contacts beyond home, work or school would need to be maintained in an exit strategy that combined isolation of cases and contract tracing with a return to work and school, there are other options. The model suggests that additional social contacts could be extended beyond 10 a day if half the workforce was able to work from home, for example.

Mr Kucharski added: “I think there is some hope. The optimistic scenario is that we’ll have more targeted and less disruptive measures, but life is going to remain pretty different for the foreseeable future, until a vaccine emerges.”