(WebMD) Pandemic swine flu doesn't worry most Americans. But that's likely to change very quickly.

Most U.S. schools will open before the fall of 2009. That's when experts warn the second wave of the pandemic may start sweeping the U.S. If that happens the U.S. -- as well as the rest of the world -- needs to be prepared for the worst. A pandemic that sickens millions could close schools and businesses, halt travel and overwhelm health care facilities.

"A pandemic is much more than a health event," said Bruce Gellin, MD, MPH, director of the National Vaccine Program Office and deputy assistant secretary of the Health and Human Services Department (HHS) to coordinate U.S. vaccination efforts. "Given the way a pandemic could play out, it has consequences across government and across society."