The United States can expect to see nearly 100,000 more COVID-19 deaths by December 1 unless people change their actions. That estimate comes from the nation’s most closely watched prediction model. Health experts say the number of deaths could be cut in half if nearly everyone wore a face covering in public spaces. These predictions show that what happens with coronavirus infections this fall depends on human behavior, said Lauren Ancel Meyers. She is director of the University of Texas COVID-19 Modeling Consortium. “We cannot stop Delta,” she said, “but we can change our behavior overnight.” That means wearing face coverings, limiting social gatherings, staying home when sick and getting vaccinated. “Those things are within our control,” Meyers said. The U.S. is in the middle of its fourth wave of infection. The highly contagious Delta variant of the coronavirus is partly to blame. It has caused a sharp rise in cases, hospitalizations and deaths, and has set back months of progress against the virus. In the U.S., deaths are now above 1,100 a day on average. The number has not been that high since the middle of March. Experts with the University of Washington predict that 98,000 more Americans will die by the start of December. That will make the total number of U.S. deaths nearly 730,000. The prediction says deaths will rise to nearly 1,400 a day by the middle of September, then lessen slowly. But the model also says many of those deaths can be avoided if enough Americans change their ways. “We can save 50,000 lives simply by wearing masks. That’s how important behaviors are,” said Ali Mokdad. He is a professor of health metrics sciences at the University of Washington and is involved in making the predictions. There are already signs that Americans are taking the threat more seriously. In the past several weeks, the demand for COVID-19 vaccine shots has gone up. The number of shots given each day has climbed around 80 percent over the past month to an average of about 900,000.