The federal government is telling the states it's time to come up with a plan for vaccinating people against swine flu.

Officials are bracing for a resurgence of the disease. They expect swine flu vaccinations to be ready this fall.

President Barack Obama says the goal is to promote "vigilance and preparation," not panic. He spoke by telephone to the National Institutes of Health, where his Cabinet officials are leading a swine flu summit with 500 state and local officials.

Health and Human Services Secretary Kathleen Sebelius told the meeting that studies with experimental doses of a swine flu vaccine are set to start in early August, to see if they're safe and seem to work. If all goes well, the vaccine could start to roll out in mid-October.

Only limited amounts of vaccine will be available at first, so Sebelius says planning will be required to make sure the right people get the shots.