Description: The proof of concept model represents the dynamics of a SIR like model in which the interaction rate of recovered individuals is enhanced compared to that of susceptible individuals. As a result, the recovery and identification of seropositive individuals can help mitigate against further transmission, significantly reducing total epidemic size compared to baseline. The extent to which shield immunity reduces spread depends on the strength of shielding and baseline epidemiological parameters, here adapted for the specific case of Covid-19.