Local protection bubbles: an interpretation of the decrease in the velocity of coronavirus's spread in the city of Sao Paulo

Pinto, J. P. G.; Magalhaes, P. C.; Figueiredo, G. M.; Alves, D.; Segura-Angel, D. M.

After four months of dealing with the pandemic, the city of Sao Paulo entered a phase of relaxed social-distancing measures in July 2020, and saw its social isolation rate fall at the same time as the number of cases, deaths, and hospital bed occupation declined. We use a calibrated multi-agent model to describe these dynamics. We assert here that this phenomenon can be understood as the result of local protective bubbles formed in the city's sub-environments at the same time that there was an exhaustion of contagion networks. Both reduce the velocity of the virus's spread, causing temporary reductions in the epidemic curve, albeit in an unstable equilibrium. These local bubbles can burst anytime and anywhere due to the reintroduction of a few infected people at the same time that there is a reduction in non-pharmaceutical interventions (NPI), such as social-distancing practices. It is important to stress that this hypothesis aligns with the dynamics of the virus's spread observed so far, without needing ad hoc suppositions about natural collective immunity thresholds or heterogeneity in the population's transmission rate, which come with the risk of making mistaken predictions that may could lead to the loss of many lives. The safe way to move ahead is to continue doing all we can to avoid new infections until a vaccine is found that properly and safely creates herd immunity.