Swine flu factor

Chicago is bracing for the return of swine flu to keep back-to-school from becoming back-to-sick.

Children -- the flu's prime spreaders -- are starting to return to classrooms in the area and across the nation.

But the swine flu vaccine won't be available until October.

And only this week will U.S. researchers start blood tests on test patients who received early vaccinations. The tests will answer how many doses of swine flu vaccine are needed for protection. That will determine whether people need to line up for two flu shots -- one against swine flu and one against regular flu -- or three.

The world's most dominant flu strain is especially dangerous to …