SARS-CoV-2 Delta variant: A gloomy forecast for the United States

By Jocelyn Solis-MoreiraAug 18 2021

The emergence of the Delta variant (B.1.617.2) in the United States has backtracked many plans to return to a pre-COVID era. A surge in COVID-19 cases due to the Delta variant has caused a rise in COVID-19 deaths and hospitalizations after what was previously a steady decline during the summer.

New research led by Benjamin P. Linas of Boston Medical Center at Boston University School of Medicine simulated the impact the Delta variant will have on the United States.

Since July 31, the Delta variant makes up 82% of coronavirus cases in the United States. The study findings suggest the United States is on course to have Delta become the dominant coronavirus variant in every state.

Given low vaccination rates and reducing social distancing behavior in many states — including in Idaho, Washington, Montana, and more — the number of daily deaths is expected to rise in at least 40 states.

“Our hope is that the findings of this report serve a warning sign and people revert to wearing masks and maintain social distancing to reduce COVID-19 associated deaths in the U.S,” wrote the researchers.

The study “Changing Dynamics of COVID-19 in the U.S. with the Emergence of the Delta Variant: Projections of the COVID-19 Simulator” is published on the preprint medRxiv* server.

The predicted number of Delta-related cases and death is constantly changing as states take countermeasures to enforce vaccination and social distancing measures. Updated projections occur weekly and are found on the COVID-19 simulator website.

Study: Changing Dynamics of COVID-19 in the U.S. with the Emergence of the Delta Variant: Projections of the COVID-19 Simulator. Image Credit: Alexander Kirch / Shutterstock

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Modeling assumptions

The researchers modeled the trajectory of COVID-19 hospitalizations and deaths each state will experience until the end of 2021. The model took into account people’s attitudes towards mask-wearing and state vaccination rates. For vaccinated individuals, the model assumed vaccines would reduce the likelihood of getting infected by 80% with one dose and 90% with two doses.

Model-estimated daily COVID-19 deaths in each state grouped by U.S. census division. The combination of high transmissibility of the Delta variant, low vaccination coverage in several regions, and more relaxed attitude towards social distancing is expected to result in a surge in COVID-19 deaths in at least 40 states.

Expected surge in cases and hospitalizations

Modeling results suggest at least 40 states will have an increase in COVID-19 deaths. Some regions, including California, Florida, Georgia, North Carolina, and Texas, are expected to surpass 100 per day.

The daily death rate across the United States is expected to be about 1,600. Between August 1, 2021, and December 31, 2021, the research team projects an additional 157,000 COVID-19-related deaths in the United States.

To date, the United States has had over 623,000 COVID-19 deaths.

The research model predicts about 20,700 Delta-related deaths in Texas, 16,000 in California, 12,400 in Florida, 12,000 in North Carolina, and 9,300 in Georgia at the end of 2021.

Past (black) and projected (red) COVID-19 deaths in each state until December 31, 2021.

If social distancing behaviors such as mask-wearing and vaccination rates do not increase, the researchers predict states in Idaho, Maine, Montana, Nebraska, North Carolina, Oregon, Washington, West Virginia, as well as Puerto Rico will exceed their current 2021 peak of coronavirus deaths.

In contrast, the Northeast is not expected to have a significant rise in Delta-related deaths. Modeling data shows COVID-19 deaths from the beginning of August to the end of 2021 to be less than 200 in New Jersey, Massachusetts, Connecticut, Vermont, and Rhode Island.

“Because of differences in population-level immunity from previous infection and vaccination, as well as attitudes towards social distancing (e.g., mask use) across states, the Delta variant could disproportionately impact some states by causing a resurgence in cases and hospitalizations,” concluded the researchers.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.