Self-isolation, contact tracing and social distancing all needed, experts warn
To keep the COVID-19 epidemic declining, R needs to be less than one.
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 based on mathematical modelling suggests that, in the absence of a vaccine, the most effective way to maintain control of the spread of coronavirus would require a combination of factors involving changes to human behaviour.
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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, meaning that one infected person would infect two or three more people on average.
The researchers calculated that mass testing alone, with 5 per cent 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 per cent, 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 per cent, 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.
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Study author Dr Adam Kucharski, from the London School of Hygiene & Tropical Medicine, UK, 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.
Is the COVID-19 R number still a useful measure?The reproduction number – often called the R value or R number – is a measure of a disease’s ability to spread. It tells us how many people a single infected person will pass on the disease to.
The R number for COVID-19 that’s being quoted in the media and government briefings is what’s known as the ‘effective’ reproduction number. This value can go up and down.
Every disease also has what’s called a ‘basic’ reproduction number, R0, which is the fixed value of R if no measures are put in place. For example, measles is highly contagious, with a R0 as high as 18, while COVID-19 has a R0 of around three.
So if COVID-19 was allowed to spread through the population, an infected person would, on average, give the disease to three other people.
But if all these people are practising physical distancing, then the virus can’t spread so easily and the effective R value goes down.
The crucial thing is to keep R below 1. If we can do this, then the number of new cases dwindles and the outbreak will eventually come to a halt.
Conversely, if R rises above 1, then we run the risk of rapidly escalating case numbers that would require stronger measures to keep the virus under control.
Because of this, R is used by governments to assess how we are doing in our efforts to stop the spread of COVID-19, and to adjust our actions, if needed.