Two new modeling papers look at the role of social distancing in #COVID19 mitigation and control in the US. Very timely given the current policy debates around whether, and how long social distancing has to be maintained here.
The first paper (from Harvard), models the progression of COVID19 in the US under various social distancing intensities and time periods. Authors look at “seasonal forcing” to include the effects of spring turning to summer turning to fall and winter. dash.harvard.edu/handle/1/42638…
Authors look first a “one-time” social distancing scenarios that reduce R0 by 20%, 40%, and 60%, over 4 week, 8 week, and 20 week periods. Authors find these one-time measures push the peak out, but epidemic comes back strongly after social distancing is stopped. 
“A single period of social distancing will not be sufficient to prevent critical care capacities from being overwhelmed…because it leaves enough of the population susceptible that a rebound in transmission after the end of the period will lead to an epidemic”
They also examine “intermittent” social distancing policies, that are imposed only when a threshold level of cases is crossed, then relaxed when the cases return below the threshold level. Under this scenario, social distancing is in place 25%-70% of the time.
Intermittent social distancing reduces the epidemic peaks and strain on critical care bed capacity. However, these measures have to be in place intermittently through 2022, as the epidemic continues over that whole time.
Authors say good surveillance data is essential for effective intermittent social distancing: “it will be necessary to carry out widespread surveillance to monitor when the prevalence thresholds that trigger the beginning or end of distancing have been crossed.”
Authors also say social distancing can reduce the prevalence of COVID-19 enough to “shift strategy to contact tracing and containment efforts, as has occurred in many parts of China”. But those countries have to be ready for resurgences, especially in winter.
Best outcomes come from either 1) intermittent social distancing in the presence of excellent surveillance information and 2) imposition of aggressive case finding and isolation practices once epidemic spread has been interrupted by social distancing of 8+ weeks.
The second paper, from an international group of authors (Spain, Italy, and US) looks at the effects of six six different social distancing approaches on COVID19 in Boston MA, specifically, if applied for 15, 30, 60, and 90 days. covid-19-sds.github.io/assets/pdfs/Pr…
The authors find that the most successful strategy for reducing the number of cases is a combination of school closures and 90% reduction in social contacts.
Regardless of which set of social distancing is put in place, the epidemic returns once they are lifted. Authors state that “passive social distance strategies are not enough to contain the epidemic”. And they argue that “active strategies need to be established”.
Active strategies in this case refer to aggressive testing, monitoring individuals’ symptoms remotely, isolation and contact tracing. Social distancing provides the initial window for implementation of these more aggressive measures.
Here's @aaronecarroll and @ashishkjha writing in the Atlantic today, arguing for this very approach. theatlantic.com/ideas/archive/…
