Abstract
In the absence of a national strategy in response to the COVID-19 pandemic, many public health decisions fell to local elected officials and agencies. Outcomes of such policies depend on a complex combination of local epidemic conditions and demographic features as well as the intensity and timing of such policies and are therefore unclear. To use a decision analytical model of the COVID-19 epidemic to investigate potential outcomes if actual policies enacted in March 2020 (during the first wave of the epidemic) in the St Louis region of Missouri had been delayed. A previously developed, publicly available, open-source modeling platform (Local Epidemic Modeling for Management & Action, version 2.1) designed to enable localized COVID-19 epidemic projections was used. The compartmental epidemic model is programmed in R and Stan, uses bayesian inference, and accepts user-supplied demographic, epidemiologic, and policy inputs. Hospital census data for 1.3 million people from St Louis City and County from March 14, 2020, through July 15, 2020, were used to calibrate the model. Hypothetical delays in actual social distancing policies (which began on March 13, 2020) by 1, 2, or 4 weeks. Sensitivity analyses were conducted that explored plausible spontaneous behavior change in the absence of social distancing policies. Hospitalizations and deaths. A model of 1.3 million residents of the greater St Louis, Missouri, area found an initial reproductive number (indicating transmissibility of an infectious agent) of 3.9 (95% credible interval [CrI], 3.1-4.5) in the St Louis region before March 15, 2020, which fell to 0.93 (95% CrI, 0.88-0.98) after social distancing policies were implemented between March 15 and March 21, 2020. By June 15, a 1-week delay in policies would have increased cumulative hospitalizations from an observed actual number of 2246 hospitalizations to 8005 hospitalizations (75% CrI: 3973-15 236 hospitalizations) and increased deaths from an observed actual number of 482 deaths to a projected 1304 deaths (75% CrI, 656-2428 deaths). By June 15, a 2-week delay would have yielded 3292 deaths (75% CrI, 2104-4905 deaths)-an additional 2810 deaths or a 583% increase beyond what was actually observed. Sensitivity analyses incorporating a range of spontaneous behavior changes did not avert severe epidemic projections. The results of this decision analytical model study suggest that, in the St Louis region, timely social distancing policies were associated with improved population health outcomes, and small delays may likely have led to a COVID-19 epidemic similar to the most heavily affected areas in the US. These findings indicate that an open-source modeling platform designed to accept user-supplied local and regional data may provide projections tailored to, and more relevant for, local settings.
Highlights
In the absence of vaccines or highly efficacious treatment, many communities in the US undertook social distancing—a reduction in person-to-person contact—to mitigate the initial spread of COVID-19 in the spring of 2020
A model of 1.3 million residents of the greater St Louis, Missouri, area found an initial reproductive number of 3.9 (95% credible interval [CrI], 3.1-4.5) in the St Louis region before March 15, 2020, which fell to 0.93 (95% CrI, 0.88-0.98) after social distancing policies were implemented between March 15 and March 21, 2020
Sensitivity analyses incorporating a range of spontaneous behavior changes did not avert severe epidemic projections. The results of this decision analytical model study suggest that, in the St Louis region, timely social distancing policies were associated with improved population health outcomes, and small delays may likely have led to a COVID-19 epidemic similar to the most heavily affected areas in the US
Summary
In the absence of vaccines or highly efficacious treatment, many communities in the US undertook social distancing—a reduction in person-to-person contact—to mitigate the initial spread of COVID-19 in the spring of 2020. Beginning on March 13, 2020, St Louis City and County enacted a number of such policies to limit the size of gatherings and reduce business traffic, which culminated in a shelter-in-place order that went into effect March 23, 2020. Because the severity of the COVID-19 epidemic in a locality such as St Louis is likely to differ, perhaps markedly, from a regional or national average, mathematical modeling studies that provide national, global, or statewide projections under different scenarios shed relatively little light on local policy effects (eg, in St Louis).[1] Comparisons to areas without social distancing policies can provide insights; those places likely differ in ways (eg, in behavior and mobility) that make them a poor proxy for what would have happened, even with statistical adjustments. As the current epidemic continues to wax and wane, and as we prepare for future pandemic crises, some quantification of the outcomes of past difficult policy decisions is needed to inform future actions
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