Controlling COVID-19 spread using instant digital contact tracing



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Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) has the potential for causing a long-lasting global pandemic. As no vaccines are available yet, instant contact tracing, coupled with quarantine and social distancing, appears to be a more plausible way of protecting the population.
In a new study published in the journal Science, a group of scientists from the University of Oxford have developed a mathematical model to study the key parameters of SARS-CoV-2 spread. They compared four routes by which the virus can be transmitted: via symptomatic individuals, via those who are yet to show symptoms (pre-symptomatic), via those who never show symptoms (asymptomatic) and via contaminated surfaces. According to this model, pre-symptomatic transmission appears to play a major role in increasing the number of infections, and may account for one-third to one-half of transmissions.

In epidemiology, the basic reproductive number (R0) is defined as the expected number of infections caused by an infected individual in the absence of widespread immunity. Sustained epidemic suppression involves bringing R0 down to less than 1, which will allow the epidemic to subside. Based on complex calculations, the researchers suggest that achieving sustained epidemic suppression for COVID-19 may not be possible by manual contact tracing alone, as it takes a lot of time, during which the disease may spread even further via pre-symptomatic individuals. 

The study instead recommends the use of a mobile phone app that builds a memory of the proximity contacts of the user. If the user develops symptoms of COVID-19 at some point, all their close contacts are notified immediately and anonymously. The notified people can isolate themselves and minimise the chances of spreading the infection.
The users of this mobile app can be traced through low-energy Bluetooth connections. When the user makes a request for the app-based SARS-CoV-2 test and tests positive, the diagnosis will be communicated to a central server. Server-transmitted signals will trigger an instant notification to other users who have been in close contact with the user who has tested positive.

Use of such a phone app can thus speed up the process of contact tracing, avoiding the delay involved in manual contact tracing, and has better potential to suppress the COVID-19 epidemic, the researchers suggest.

However, the researchers also acknowledge that the use of such an app raises ethical questions regarding access, transparency and protection of personal data of the user.
The team has also developed a web interface that they plan to update as and when new data becomes available and the epidemic evolves, which will serve as an on-going resource for further research.

Stuti Mohapatra is currently pursuing doctoral studies in Neurovirology at the National Brain Research Center, Manesar