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Social isolation relaxation and the effective reproduction number (Rt) of COVID-19 in twelve Brazilian cities.

We analyzed the social isolation relaxation strategies adopted by the twelve biggest Brazilian cities in 2020, in relation to the number of cases, number of deaths and the effective reproduction number (Rt), which are internationally considered the fundamental epidemiological criteria for allowing wider population mobility in public spaces. The Brazilian central government has not set unique guidelines neither for closure nor for opening, and states and cities have taken the lead in strategy definition. Until July 31 2020, in Belém do Pará, Fortaleza, Manaus, Recife and Rio de Janeiro, where the epidemic peak had already been surpassed, and in Salvador and São Paulo, in which the peak seemed to be already reached, the Rt curve followed a decreasing path after the openings. Porto Alegre, a city in which the epidemic curve was flattened, had an increase in Rt after the start of relaxation. In Belo Horizonte, Brasília, Curitiba and Goiânia, where the curve was also flattened, the Rt remained stable after the opening. The decision on how to operationalize the relaxation of social isolation and the speed with which it happened was heterogeneous among the cities studied. Also, broad population testing strategies were not done in any of the cities.