The COVID-19 pandemic has highlighted the importance of disease models for situational awareness, decision-making, and planning. From weather to infectious diseases, it has been shown that synthesizing results from multiple models gives more reliable projections than results from any one model alone. Single model projections are particularly problematic for emerging infections where there is considerable uncertainty about basic epidemiological parameters (such as the proportion of asymptomatic individuals, and the waning of immunity), the transmission process, future policies and their impact, and population behavior. Combining outputs from multiple models can be particularly crucial for scenario projections several months into the future; scenario projections address what could happen under a particular set of circumstances (including but not limited to interventions, changes in disease epidemiology, and/or population behavior). was created in December 2020 to provide multiple rounds of real-time, long-term scenario projections in the US for the federal and local health authorities, other decision makers and public health experts, and the general public. Notably, scenario hub projections were used to guide the expansion of the in 2021, and in fall 2022.
