Within the US, states and cities have established various COVID-19 alert systems. New Zealand, Singapore, South Africa, and the UK have national systems ranging from three to five alert levels that track data on various combinations of COVID-19 incidence, hospitalizations, death, and available healthcare capacity 6, 7 the alert-level system in South Africa includes both economic and public health considerations, while the systems in New Zealand and Singapore focus on public health alone.
France, for example, has a four-stage system the maximum level is triggered when weekly regional COVID-19 incidence exceeds 250 infections per 100,000 people and COVID-19 patients in the intensive care unit (ICU) occupy at least 60% of capacity 5. Although most systems include intermediate levels that are intended to slow transmission and reduce the need for full-blown shelter-in-place orders, they vary considerably in complexity, key indicators, and policy levers. They typically monitor one or more data streams-such as COVID-19 case counts, test positivity, hospital capacity, or deaths-and trigger changes in alert level when the data reach specified thresholds 4. Governmental bodies worldwide have established a variety of COVID-19 alert systems to provide situational awareness and policy directives for the public. In the US-which has reported over 583,000 COVID-19 deaths as of 3-communities have scrambled to tighten and relax mitigation policies in response to threatening surges in hospitalizations. Within two months, however, many regions lifted restrictions hoping to alleviate socioeconomic hardship, although the risks of resurgence were high 1, 2. By April of 2020, strict stay-home orders were enacted almost universally to combat initial waves of transmission. Along with viral testing, strategies such as social distancing, face-mask ordinances, business closures, travel restrictions, and stay-home orders have remained paramount, even as safe and efficacious vaccines have become widely available and utilized. Throughout the COVID-19 pandemic, community mitigation activities have proved vital to slowing viral transmission and ensuring the integrity of healthcare systems.
As cities worldwide face future pandemic waves, our findings provide a robust strategy for tracking COVID-19 hospital admissions as an early indicator of hospital surges and enacting staged measures to ensure integrity of the health system, safety of the health workforce, and public confidence. As proof-of-concept, we describe the optimization and maintenance of the staged alert system that has guided COVID-19 policy in a large US city (Austin, Texas) since May 2020. In comparison, we show that other sensible COVID-19 staging policies, including France’s ICU-based thresholds and a widely adopted indicator for reopening schools and businesses, require overly restrictive measures or trigger strict stages too late to avert catastrophic surges. With public compliance, the policy triggers ensure adequate intensive care unit capacity with high probability while minimizing the duration of strict mitigation measures.
We derive optimal strategies for toggling between mitigation stages using daily COVID-19 hospital admissions. Judicious implementation and relaxation of restrictions amplify their public health benefits while reducing costs. Community mitigation strategies to combat COVID-19, ranging from healthy hygiene to shelter-in-place orders, exact substantial socioeconomic costs.