Using random testing to manage a safe exit from the COVID-19 lockdown

Markus Mueller; Peter Derlet; Christopher Mudry; Gabriel Aeppli

The COVID-19 pandemic has led to a worldwide shutdown of a major part of our economic and social activities. This political measure was strongly suggested by epidemiologic studies assessing the cost in human lives depending on different possible policies (doing nothing, mitigation, suppression) [1] [2] [3] [4] . Mitigation can be achieved by combinations of different measures, including physical distancing, contact tracing, restricting public gatherings, and the closing of schools, but also the testing for infections. The quantitative impact of very frequent testing of the entire population for infectiousness has been studied in a recent unpublished work by Jenny et al. in Ref. [5] . We will estimate in Sec. III that to fully suppress the COVID-19 pandemic by widespread testing for infections, one needs a capacity to test millions of people per day in Switzerland. This should be compared to the present number of 7'000 tests per day across Switzerland. 1 Here we suggest that by testing a much smaller number of randomly selected people per day one can obtain important quantitative information on the rates of transmission, so as to enable well-informed decisions. Figure 1 summarizes the key concept of the paper, namely a feedback and control model for the pandemic. The essential output from random testing is the growth rate of the number of currently infected people, which it-self is regulated by measures such as those enforcing physical distances between persons (physical distancing), 2 and whose tolerable values are fixed by the capacity of the health-care system. A feedback and control approach [6] , familiar from everyday implementations such as thermostats regulating heaters and air conditioners, should allow policy makers to damp out oscillations in disease incidence which could lead to peaks in stress on the healthcare system as well as the wider economy. Any other measurement of the fraction of currently infected people can replace the random testing, for example there are proposals to estimate this fraction from analysis of sewage water with PCR tests [7, 8] .