With Delta variant dominance, simulator predicts surge in COVID-19 deaths in most of U.S.

BOSTON – Investigators who previously developed the COVID-19 Simulator (www.covid19sim.org)—which models the trajectory of COVID-19 in the U.S. at the state and national levels—have applied the tool to analyze potential scenarios in which the COVID-19 Delta variant becomes dominant in every state. The analysis, which is published on the preprint server medRxiv, reveals that the combination of high transmissibility of the Delta variant, low vaccination coverage in several regions, and more relaxed attitudes toward social distancing will likely lead to a surge in COVID-19–related deaths in at least 40 states.

The simulator also predicts that in several states, daily COVID-19–related deaths could exceed the peak daily deaths that occurred in early 2021 if current social distancing behaviors and vaccination rates remain unchanged.

An additional 157,000 COVID-19–related deaths could occur across the United States between August 1 and December 31, 2021. The model projects approximately 20,700 COVID-19–related deaths in Texas, 16,000 in California, 12,400 in Florida, 12,000 in North Carolina, and 9,300 in Georgia during this period. In contrast, the projected number of COVID-19–related deaths would remain below 200 in New Jersey, Massachusetts, Connecticut, Vermont and Rhode Island.

The team’s projections are updated weekly by incorporating vaccination rates and social distancing measures in each state, and the latest results can be found at the COVID-19 Simulator website.

“These projections should serve as a warning sign, especially in states that could have higher daily COVID-19 deaths than their previous peaks,” says lead author Jagpreet Chhatwal, PhD, associate director of Massachusetts General Hospital’s Institute for Technology Assessment and an assistant professor at Harvard Medical School. “We also hope that our projections can help policymakers bring back mask mandates and further advocate for COVID-19 vaccines.”

Senior author Benjamin P. Linas, MD, MPH, a professor of medicine at Boston University School of Medicine, adds that although it was hoped that the pandemic was waning, additional action is needed. “If you are not vaccinated, you are at high risk because of the Delta variant. August 2021 is potentially more dangerous to you than August 2020,” he says. “If you are vaccinated, you are much safer, but you should still care about this ongoing transmission because it creates the circumstances that generate new variants. If we want to end this pandemic, then all Americans need to be vaccinated and at least right now, we should be masking when in public indoor spaces.”

Co-author Jade Yingying Xiao, a PhD student at Georgia Tech, notes that if recent estimates of the reproduction number of the Delta variant are correct, then the team’s model implies current levels of social distancing are reducing transmission by 30% to 40%. “We can easily foresee this number dropping as we move ahead into the fall months with schools and colleges reopening,” she says.

Co-authors include Peter Mueller, Turgay Ayer, Madeline Adee, Ozden O. Dalgic and Mary Ann Ladd.

About the Massachusetts General Hospital
Massachusetts General Hospital, founded in 1811, is the original and largest teaching hospital of Harvard Medical School. The Mass General Research Institute conducts the largest hospital-based research program in the nation, with annual research operations of more than $1 billion and comprises more than 9,500 researchers working across more than 30 institutes, centers and departments. In August 2021, Mass General was named #5 in the U.S. News & World Report list of "America’s Best Hospitals."