"We want to make sure we are not promoting panic but we are promoting vigilance and preparation," President Barack Obama said in a phone call from Italy to the National Institutes of Health, where his Cabinet officials were leading a swine flu summit with 500 state and local officials.

No final decision has been made on vaccination, Health and Human Services Secretary Kathleen Sebelius told the meeting.

But studies with experimental doses of the new swine flu vaccine are set to start in early August, to see if they're safe and seem to work. If all goes well, some vaccine could start to roll out in mid-October, she said.

Probably first in line for shots would be school-age children, young adults with risky conditions like asthma, pregnant women and health workers, she added.

"We need your help now to prepare" so those shots actually get to people's arms, Sebelius told state officials.

Only limited amounts of vaccine will be available at first, but she warned that even a modest vaccination campaign "will involve extraordinary efforts throughout this country."

Swine flu may have faded from the headlines but it's still sickening people in the U.S. and especially abroad and is almost certain to worsen when influenza-friendly fall temperatures arrive.

"We must avoid complacency," Sebelius said.

The government estimates that 1 million Americans so far have been infected with the never-before-seen virus known formally by its scientific family name, H1N1.

No longer do many public health experts warn of the new virus' "return" in the fall. Summer's heat and humidity usually chase away influenza, but the swine flu has never left. Children are spreading it in summer camps - 50 outbreaks documented so far - and U.S. deaths have reached 170.

It has spread worldwide, and is causing serious problems in parts of the Southern Hemisphere, where it's currently flu season.

In the U.S., even if the virus doesn't mutate to become more dangerous, greater spread is considered inevitable as students return to crowded classrooms and temperatures drop - and regular winter flu makes its own return.

"This fall, it's daunting, all that will be required," said Paul Jarris, executive director of the Association of State and Territorial Health Officials.

At the top of his worry list is finding enough workers for two vaccination campaigns.

The 100 million-plus doses of regular winter flu vaccine are set for the usual October inoculation start. But those shots won't protect against swine flu.

Looking back at school closings that disrupted the spring, communities also are struggling to determine when such a drastic step - one that has the chain reaction of parents missing work - is necessary.

A key theme to Thursday's summit: Consider now how your family would handle a disruption even bigger than what happened last spring when the outbreak began. To spur those discussions, HHS will host a contest - at http://www.flu.gov - for the best anti-flu video to turn into a national public service announcement.

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