Current epidemiology research on COVID-19 shows that contact tracing is only able to curb the growth of the epidemic, if we identify 50% of the positive cases and trace 60% of their contacts with no delay. If we take more than three days to quarantine contacts, the growth of the epidemic cannot be controlled. This puts enormous strain and pressure on manual contact tracing regimes to meet these tight requirements and provides motivation for other more automated tools that use smartphones or some other means to help provide faster notification times. In countries like South Africa that have a dual economy with high income inequality and unemployment, there is no one-size-fits-all solution to contact tracing. Most automated contact tracing hinges on owning a smartphone and having Internet access, but Smartphone ownership and Internet access is limited. Current estimates are that between 49 and 52% of the rural population and between 63 and 69% of the urban population own a smartphone. A national contact tracing system that depends on smartphone ownership alone would leave a large section of the population (mostly the low-income portion of the population) locked out of the contact tracing programme. There is an argument to be made for smartphone-based contact tracing in urban areas due to its higher smartphone penetration. The effectiveness of a smartphone application in detecting person to person encounters follows a square law where the number of encounters is asymptotically proportional to the square of fraction of the population using the application. If a contact tracing application was installed on smartphones in urban areas and we achieved close to 100% uptake (approximately 60% of the population that have smartphones with the required contact tracing features); we would detect approximately 36% of the contacts made. Epidemiology models show us that this level of contact detection would require 80%1 of the cases to be detected with immediate notification and isolation to have an impact on reducing the spread of the virus. This is a tough target and provides motivation for a better approach that uses a combination of multiple contact tracing regimes (manual and automated) that all have an underpinning theme of being privacy-preserving.
