Modeling Exit Strategies from COVID-19 Lockdown with a Focus on Antibody Tests

Reinhard German; Anatoli Djanatliev; Lisa Maile; Peter Bazan; Holger Hackstein

Note that the two states was_asymptomatic and was_symptomatic are split into 4 stocks: wasAsymp_AB_unknown, wasAsymp_AB_known, wasSymp_AB_unknown, and wasSymp_AB_known, in order to separate between cases where recovered persons have ABs but this is not known vs. cases in which it is known because of AB tests. In case of asymptomatic and recovered persons this is completely unknown and in case of symptomatic and recovered persons it can be supposed that they have ABs but without certainty. There is also an additional stock to represent infections coming from outside. The stock Regeneration is only implemented to account for the fact that people are considered as recovered with a delay. It is used since patients after being sick cannot directly participate in public life and its duration is set to 5 days to reflect values in Germany. However, it can as well be omitted, since it only delays statistics for recovered people. Flow F Au corresponds to true positive AB tests of recovered with ABs who were asymptomatic whereas flow F Su corresponds to those who were symptomatic. For the corresponding flow rates factors need to be computed consisting of the sensitivity, the proportion of the outgoing stock, and the weight mentioned in Sec. 3. These factors need to be normalized and multiplied with the available test rate, for details please check the Appendix.