Confinement time required to avoid a quick rebound of COVID-19: predictions from a Monte Carlo stochastic model

How long should we self-isolate at home to diminish the threat of COVID-19? This is a question that billions of people are wondering early 2020 due to the outbreak of the novel coronavirus SARS-CoV-v2. This virus can produce a severe pneumonia that has killed tens over 210,000of thousands of people so far, was detected for the first time late 2019 in Wuhan (China), and has spread all over the world due, in part, to the difficulty of detecting and isolating asymptomatic or mild-symptomatic cases. In this paper, we explore how long suppression strategies (i.e., home confinement and social distancing) must be put into practice in highly populated cities to reduce the chances that a quick rebound of COVID-19 cases occur again over the next months. This is explored, using New York City (USA), San Francisco (USA), and Madrid (Spain) as case studies, through a simple but realistic Monte Carlo stochastic model that takes into account that part of the undetected infected individuals remain in circulation propagating the virus. Our simulations reflect that, if suppression strategies are not properly applied, they can be counterproductive because there are high chances that the confinement time has to be lengthened without reducing the total number of infections. We also find estimate that, in the most conservative scenario and under the model assumptions, home confinement is effective if applied at least ~110 days in New York City, ~80 days in San Francisco, and ~70 days in Madrid, i.e., until mid-July 2020, early June 2020, and late May 2020, respectively.