• Stephen Grice

The Effect of Social distancing, Isolation and Digital Contact Tracing on COVID-19

Updated: May 16

We have completed some research into how New Zealand and other countries can minimize the cost of COVID-19 to society. To do this we have developed SIR equations that model social distancing, isolation and digital contact tracing.


The central question is what mix of policies are required to reduce the effective reproduction number Reff < 1 and stop the epidemic? The answer is contained in this technical report.


All three policies (social distancing, quarantining, and contact tracing) are required to get Reff<1, according to our calculations, and the polices work together to suppress the disease.


Trade-offs can be made. Cost is an important factor, and of the three policies, social distancing carries substantially the greatest costs.


Which raises the question: what is the optimal combination of these policy settings? When analyzing this mix of policies (and hence variables), we would opt for the most liberal social distance measures, reflected in a choice of R0 = 2.5. Strict but reasonable quarantining measures are defined by q= 0.2. This combined with digital contact tracing that goes back at least 6 days


So the answer... is that if you:

  • have a minimum of social distancing, which is represented by the basic reproduction number of R0 = 2.5,

  • isolate at least 80% of those that test positive effectively

  • use digital contract tracing to quickly isolate individuals that have been in contact with an infected individual in the last 6 days

then we can achieve Reff < 1 and suppress the epidemic for COVID-19.

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