When will the pandemic end? Should we wear face masks? When could it have ended had different policy decisions been made? These are the questions that my research team at the University of South Florida’s Department of Industrial Engineering has been seeking to answer.

We used a detailed computer simulation model to obtain trajectories of actual and reported number of infected cases and deaths for the biggest urban epicenter of cases in Florida — Miami-Dade County (population 2.8 million). Here is what we found.

What would have happened if we all stayed in lock-down with stay-at-home order?

The model showed that the pandemic would have ended by Aug. 1, with about 160,000 infected (5.8 percent of the Miami-Dade population), 4,100 hospitalized, and 1,000 dead; the actual numbers as of July 3 were 4,112 hospitalized and 1,034 dead. In this scenario, we could potentially see a later reemergence of COVID-19. This risk could be minimized with a follow-up plan comprising the use of face masks, contact tracing and widespread testing.

What would have happened if we had stayed in Phase I of reopening (businesses and restaurants operate with up to 50 percent capacity, bars closed, etc.)?

The model showed that the pandemic would stretch well beyond the year 2020, ending with herd immunity around June 25, 2021, with 628,000 infected, 40,000 hospitalized and 10,000 dead.

What happens if the current Phase II of reopening continues (businesses and restaurants operate with up to 75 percent capacity, bars open with 50 percent capacity, etc.)?

The model showed that herd immunity would end the pandemic around mid-October of 2020 but not without a devastating 2.2 million (80 percent of population) infected, 150,000 hospitalized and 36,000 dead.

What if we all wear face masks (and continue with Phase II)?

Surgical grade face masks are estimated to reduce virus sharing by about 65 percent. When used together with the Phase II order, it produced a reduction of about 470,000 (21 percent) in total infected, 30,000 (20 percent) in total hospitalized and 6,000 (17 percent) in total deaths. The pandemic would end with herd immunity by Nov. 12.

What if we wear face masks and use aggressive contact tracing (and continue with Phase II)?

An aggressive contact tracing (with the goal to identify 50 percent of the asymptomatic and pre-symptomatic), if implemented starting today, while continuing Phase II and use of face masks, showed significant positive impact. Outbreak will end in late September with a 63 percent reduction in total infection (saving around 1.1 million, 40 percent of population) compared to Phase II and face masks alone. Hospitalizations and deaths will also be reduced by 68 percent.

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The simulation model replicated hour by hour social interaction behavior at home, school, work and community places for each of 2.8 million people. The model considers a large number of parameters to account for census reported demographics (of households and workplaces), virus characteristics, and the social interventions.

The model begins with a few infected cases with travel histories. Mixing of these cases starts the community infection process. The model is calibrated to replicate state-reported values for infections and deaths. Simulated infected cases follow the COVID-19 disease process leading to health outcomes of asymptomatic, recovered or dead. The model can be applied to other U.S. urban areas.

Tapas K. Das is professor and chair of Industrial and Management Systems Engineering at the University of South Florida. The research team comprised Das; Hanisha Tatapudi, a doctoral candidate at USF; Rachita Das, an M.D. ’21 candidate at the University of Miami; and Peter Fabri, a doctor with a doctorate at USF.