Since then, the virus has infected an estimated 1 million Americans and still is spreading, remarkable considering influenza usually can’t tolerate summer’s heat and humidity.

“What I need from all of you is an idea of when it is best to close, when it is necessary to close, and when it’s not,” said Belinda Pustka, superintendent of Texas’s Schertz-Cibolo-Universal City Independent School District.

“Closing school is a last resort, not a first resort,” Duncan stressed, but he said schools need to plan how they’ll keep students learning if they do have to close for extended periods.

Pustka’s schools posted assignments online. But Sue Todey of Wisconsin’s Department of Public Education said that between rural geography and poverty, many students don’t have the necessary internet access, and she’s exploring using public television or old-fashioned sending home of paper assignments.

An even bigger problem: When schools close and working parents need to stay home–or any worker gets sick–too often, they don’t get paid, said Paul Jarris of the Association of State and Territorial Health Officials. So they come to work, spreading infection.

“How are we going to assist people who don’t have benefits?” he asked.

Homeland Security Secretary Janet Napolitano said she was working with the Labor Department to address that question, and she urged employers to allow telecommuting and make other provisions should swine flu hit their workplaces this fall.

Swine flu outbreaks in the fall are all but certain, given its continued spread here–50 outbreaks in children’s summer camps as of press time–and abroad, with major problems in parts of the Southern Hemisphere.

What doctors can’t predict is how bad it will be during the U.S. flu season, but Obama’s team of heavy-hitters spent July 9 warning against complacency.

Even if swine flu proves no more deadly than regular winter flu, that kills 36,000 Americans a year–and with swine flu, teenagers and young adults are being disproportionately hit, said Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention. And both types could very well spread at the same time this fall.

“If it doesn’t happen, we’ll be fortunate,” Sebelius added.