Evaluating a Public Health Assessment and Response Framework: SARS-CoV-2 Spread Under the Controlled Distancing Model of Rio Grande do Sul, Brazil.

Abstract

In early 2020, to halt the spread of SARS-CoV-2, the state government of Rio Grande do Sul in Brazil established a public health assessment and response framework known as a "controlled distancing model." Using this framework, the government divided the state into 21 regions and evaluated them against a composite index of disease transmission and health service capacity. Regions were assessed using a color-coded scale of flags that was updated on a weekly basis and used to guide the adoption of nonpharmaceutical interventions. In this study, we aimed to evaluate the extent to which the controlled distancing model accurately assessed transmission and the effectiveness of its responses throughout 2020. We estimated the weekly effective reproduction number (R_t) of SARS-CoV-2 for each region using a renewal equation-based statistical model of notified COVID-19 deaths. Using R_t estimates, we explored whether flag colors assigned by the controlled distancing model either reflected or affected SARS-CoV-2 transmission. Results showed that flag assignments did reflect variations in R_t to a limited extent, but we found no evidence that they affected R_t in the short term. Medium-term effects were apparent in only 4 regions after 8 or more weeks of red flag assignment. Analysis of Google movement metrics showed no evidence that people moved differently under different flags. The dissociation between flag colors and the propagation of SARS-CoV-2 does not call into question the effectiveness of nonpharmaceutical interventions. Our results show, however, that decisions made under the controlled distancing model framework were ineffective both at influencing the movement of people and halting the spread of the virus.