WASHINGTON — Schools should be ready with hard-copy packets and online lessons to keep learning going even if swine flu sickens large numbers of students, U.S. Secretary of Education Arne Duncan said Monday.

Speaking at an elementary school on the first day of classes in Washington, Duncan released recommendations on how educators can ensure instruction continues should the virus cause high absenteeism or school closings.

"As the school year begins, I'm concerned that the H1N1 virus might disrupt learning in some schools across the country," he said.

Duncan said schools should evaluate what materials they have available for at-home learning. The latest guidance provides more details on methods schools could use, such as distributing recorded classes on podcasts and DVDs; creating take-home packets with up to 12 weeks of printed class material; or holding live classes via conference calls or "webinars."

Federal officials said earlier this month schools should close only as a last resort. They also advised that students and teachers can return to school or work 24 hours after their fever is gone; the old advice was to stay home for a week. The virus prompted more than 700 schools to temporarily close last spring.

Duncan was joined by U.S. Health and Human Services Secretary Kathleen Sebelius and representatives from several technology companies and publishers, such as Apple, Microsoft and Pearson, which are working with the Education Department to offer print and online resources, some of which could be free, to schools severely affected by swine flu. The details are still being worked out, but the companies might offer technology to allow students and teachers to communicate virtually, provide published instructional material, and provide computer servers that can handle transferring large amounts of teaching material.

Sebelius said clinical trials of the swine flu vaccine "look good" and it could possibly be administered by mid-October.

"We anticipate using schools as partners to make sure that we reach out to kids who are a priority population to get the vaccination," she said.