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Self-isolation and contact tracing ‘key to keeping Covid-19 under control’

By Nilima Marshall
Combining self-isolation and extensive contact tracing with moderate physical distancing measures could help keep the ongoing Covid-19 epidemic under control, according to experts.

New research in the UK based on mathematical modelling suggests that, in the absence of a vaccine, the most effective way to maintain control of the disease would require a combination of factors involving changes to human behaviour.

These would include keeping social distancing measures in place, such as remote working and limiting large gatherings, alongside other preventative actions such as contact tracing and self-isolation.

The team used social contact data on more than 40,000 individuals from the BBC Pandemic database.

They also modelled the reproductive number (R), which is the average number of people each individual with the virus is likely to infect at a given moment, using different scenarios.

To keep the Covid-19 epidemic declining, R needs to be less than one.

Had no control measures been put in place, R would be 2.6 in the UK, meaning that one infected person would infect two or three more people on average.

The researchers calculated that mass testing alone, with 5% of the population undergoing random testing each week, would lower R to just 2.5, as many infections would either be missed or detected too late.

Compared with no control measures, self-isolation of symptomatic cases alone would reduce transmission by around 29%, lowering R to 1.8.

But the model showed that combining self-isolation, household quarantine and tracing strategies (which would include app-based contact tracing and manual tracing of all contacts), would potentially reduce transmission by 64%, bringing R down to 0.94.

However, the researchers note that their model is based on a series of assumptions, such as quick isolation and adherence to quarantine, which they said are plausible but optimistic.

They also said that their model only includes specific settings such as home, school and work, and does not explicitly include imported infections, which may be detected at a different rate from local infections.

Study author Dr Adam Kucharski, from the London School of Hygiene & Tropical Medicine, said: “Our findings reinforce the growing body of evidence which suggests that we can’t rely on one single public health measure to achieve epidemic control.”

“Successful strategies will likely include intensive testing and contact tracing supplemented with moderate forms of physical distancing, such as limiting the size of social gatherings and remote working, which can both reduce transmission and the number of contacts that need to be traced.”

He added: “The huge scale of testing and contact tracing that is needed to reduce Covid-19 from spreading is resource intensive, and new app-based tracing, if adopted widely alongside traditional contact tracing, could enhance the effectiveness of identifying contacts, particularly those that would otherwise be missed.”

The research is published in the journal The Lancet Infectious Diseases.

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