We use COVID-19 cases, hospitalizations, and mortality data and a deterministic SEIR (susceptible, exposed, infectious and recovered) compartmental framework to model possible trajectories of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and the effects of non-pharmaceutical interventions in the United States at the state level. Our SEIR model uses several critical variables to produce these projections such as pneumonia seasonality, mobility, testing rates, population, density, mask use per capita, and vaccination levels and vaccines effectiveness. In making these forecasts, we aim to help policymakers plan for the days and months ahead, and take action to change the course of the pandemic for the better. We have developed three different scenarios that can help policymakers understand how different policy decisions, along with the availability of vaccines, could affect the trajectory of the pandemic in their location. With the surge of new variants, we have adopted our models to estimate the speed of their spread and their impact on vaccine effectiveness. Our results show that given the  available evidence on waning immunity and lower efficacy of vaccines preventing infection as compared to hospitalization and death, strategies to reduce  COVID-19  transmission  to  zero  are  unlikely to succeed. Ongoing COVID-19 transmission and burden on the health system are likely to extend past the forecast period and well into 2022 and beyond.

Learning objectives

1.    Recognize the drivers of Covid19 trends.

2.    List the short and long term scenarios given vaccine effectiveness and waning immunity.

3.    Discuss factors that would impact the trajectory.