Lancet study confirms no ‘silver bullet’ and suggests combination of physical distancing, contact tracing and self-isolation to be most effective.
Thursday, 18 June 2020, Katie Coyne
Choosing just one or two interventions will not be enough in the fight against COVID-19 – we must ‘layer up’, a Lancet study has found.
Physical distancing is needed alongside contact tracing and self-isolation if the pandemic is to be controlled, a study published in the Lancet Infectious Diseases journal has discovered.
Scientists used data collected between 2017 and 2018 from the BBC Pandemic Experiment, which recorded social contact of 40,000 participants to model how a highly infectious flu might spread.
Using this data, scientists then looked at the various interventions being used to tackle coronavirus to model how effective they were on their own, and in various combinations.
Without moderate physical distancing in place, they found very large numbers of people would need to be traced and required to self-isolate. Moderate physical distancing was defined in the study as limiting daily contact to just four individuals outside of the household. Without this measure, for every 5,000 symptomatic cases of COVID-19 between 75,000 and 205,000 contacts would need to be quarantined.
Co-author Hannah Fry said: “It uses one of the best sets that we have on how people in the UK behave, how they travel, who they meet, how often they come into contact with others. That's the richest example of how people in normal life want to behave.
“This tries to go through the various measures suggested – some of them at certain points have been thought of as a silver bullet, the app for example. It calculates what the impact and reproduction would be if that intervention were implemented.
“I [have] really come to the conclusion that the only way we're going to realistically keep the reproduction number below one is if we layer up a combination of interventions, rather than relying on one.”
However, Fry added that some interventions have a greater impact than others: “There are some things that end up making a very big difference. Even things like self-isolation, if you have symptoms, actually takes a big chunk out of the reproduction number. There are other things like people working from home, that does actually have a big impact.”
With random mass testing alone, with a testing rate of 5% of the population or 460,000 tests per day, the R rate of infection would only be reduced to 2.5. This is because so many infections would be missed or discovered too late.
Self-isolation at home of symptomatic cases by itself reduced transmission rates by 29% and lowered R to 1.8.
Combining self-isolation, household quarantine and contact tracing had a large combined impact. Combining these interventions with app-based contact tracing could reduce transmission by 47% and lower R to 1.4, while integrating with manual contact tracing of all contacts transmission is reduced by 64% and R lowered to 0.94.
The authors note that achieving such high levels of contact tracing may be difficult and add that a larger reduction in transmission of 66% could also be achieved by combining these measures with physical distancing, lowering R to a much safer 0.87.