Projected resurgence of COVID-19 in the United States in July—December 2021 resulting from the increased transmissibility of the Delta variant and faltering vaccination

Abstract

In Spring 2021, the highly transmissible SARS-CoV-2 Delta variant began to cause increases in cases, hospitalizations, and deaths in parts of the United States. At the time, with slowed vaccination uptake, this novel variant was expected to increase the risk of pandemic resurgence in the US in summer and fall 2021. As part of the COVID-10 Scenario Modeling Hub, an ensemble of nine mechanistic models produced six-month scenario projections for July-December 2021 for the United States. These projections estimated substantial resurgences of COVID-19 across the US resulting from the more transmissible Delta variant, projected to occur across most of the US, coinciding with school and business reopening. The scenarios revealed that reaching higher vaccine coverage in July—December 2021 reduced the size and duration of the projected resurgence substantially, with the expected impacts was largely concentrated in a subset of states with lower vaccination coverage. Despite accurate projection of COVID-19 surges occurring and timing, the magnitude was substantially underestimated 2021 by the models compared with the of the reported cases, hospitalizations, and deaths occurring during July-December, highlighting the continued challenges to predict the evolving COVID-19 pandemic. Vaccination uptake remains critical to limiting transmission and disease, particularly in states with lower vaccination coverage. Higher vaccination goals at the onset of the surge of the new variant were estimated to avert over 1.5 million cases and 21,000 deaths, though may have had even greater impacts, considering the underestimated resurgence magnitude from the model.

An evaluation of prospective COVID-19 modelling studies in the USA: from data to science translation

“…We included preprints from modellers participating in the US COVID-19 Forecast Hub, which focuses on 1-week to 4-week predictions. 2 We also attempted to include the Scenario Modelling Hub, 20 , 21 , 22 but no preprints met our criteria for the time window considered. Although these papers do not have the validation that comes with peer-review, these models were used in real-time by the Centers for Disease Control and Prevention (CDC), which we believe justifies their inclusion in this analysis.…”

Data-driven scalable pipeline using national agent-based models for real-time pandemic response and decision support

“…This work has been discussed in the national media and by the head of the CDC on one of their video briefings in the Summer 2021. Details about how such models are assessed and presented can be found in companion papers that consist of all participating teams of Scenario HUB ( Truelove et al, 2022 ). This paper focuses on the national agent-based models developed by our team.…”

“…The present paper is not about our modeling work; that work is covered in a companion paper ( Truelove et al, 2022 ). Here the primary focus is on the creation of a scalable workflow that allows projections to be run on a weekly basis through the integration of approximately 3100 county-level surveillance datasets.…”

Scenario Design for Infectious Disease Projections: Integrating Concepts from Decision Analysis and Experimental Design

“…The use of scenario modeling has become pervasive in infectious disease epidemiology over the last two decades. Notable examples include modeling of different types and layers of interventions to control emerging outbreaks such as foot-and-mouth disease in the United Kingdom (Tildesley et al, 2006), avian influenza (Longini et al, 2005), the Ebola outbreak in West Africa (Meltzer et al, 2014), and the COVID-19 pandemic (Borchering et al, 2023;Borchering et al, 2021;Hellewell et al, 2020;Truelove et al, 2022;Walker et al, 2020). Additional notable use cases include the roll-out of new interventions for endemic pathogens where, for instance, scenario projections can help anticipate the benefits and dynamic changes associated with new vaccines or improved drugs (Flasche et al, 2016;Pitzer et al, 2009;Eaton et al, 2012;Houben et al, 2016).…”