(AP) - Hundreds of schools scattered around the country closed as the nation's swine flu caseload passed 100 Thursday, and U.S. authorities said they eventually could produce enough vaccine for everyone if necessary - but that shots couldn't begin until fall at the earliest.

The CDC confirmed 109 cases Thursday, and state officials confirm at least 20 more. Cases now are confirmed in: New York, Texas, California, South Carolina, Kansas, Massachusetts, Indiana, Ohio, Arizona, Michigan, Nevada, New Jersey, Delaware, Colorado, Georgia, Minnesota and Virginia.

The Health and Human Services Department said late Thursday the government was buying 13 million treatment courses of anti-flu drugs to replenish the U.S. strategic stockpile and help fight the swine flu outbreak. The U.S. on Thursday also began sending 400,000 treatment courses of the drugs to Mexico to help against swine flu there.

On Wednesday, the WHO said swine flu threatened to become a pandemic, and for the first time it raised its threat level to Phase 5, the second-highest. Officials said Thursday there were no immediate signs that warranted declaring a Phase 6 pandemic.

Phase 5 means a virus has spread into at least two countries and is causing large outbreaks. Phase 6 means outbreaks have been detected in two or more regions of the world and a pandemic is under way.

The only confirmed U.S. swine flu death so far is a Mexican toddler who succumbed earlier this week in Texas. New cases of swine flu were confirmed Thursday in Europe, but no deaths have been reported outside North America.