Dr. Anthony Fauci says Alabama and other states with soaring coronavirus rates have a window of opportunity to bring it under control and spoke in favor of state and local requirements for masks in public.

Fauci, director of the National Institute of Allergy and Diseases, says the United States is in a resurgence of new coronavirus cases, with daily cases nearly double the country’s previously high baseline. Infection rates have been rising in the South and West.

“We are facing a serious problem now,” Fauci said in an online news conference with Alabama Sen. Doug Jones. He says the U.S. is in a situation where it must continue to try to reopen in a safe, prudent manner.

“What is alarming is the slope of the curve,” Fauci said of cases in Alabama. He added, “the signal should be wear a mask, period.”

Fauci says the mean age of people getting infected is about 15 years younger than previously in the U.S. While generally healthier, young people can still face serious illness if they have underling health conditions.

The country’s top infectious disease expert spoke in favor of school reopening, saying there are ripple effects for families if children can’t go to school. He says areas with high rates of illness might consider mandatory masks or rotating schedules to reduce classroom size.