Dr. Howard Markel, a pediatrician at the University of Michigan, told ABC News today that the fact that kids are more affected than adults is cause for concern. He added that among groups of students also at risk for problems like asthma or diabetes there may be added need to fine-tune closure plans.
Markel also said school closures are promising when the situation is severe but that the current threat so far doesn't merit mass closures.
"You have to make sure that the threat merits the response," he said.
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Of all cases in the U.S., more than 5,500 people have been hospitalized and 353 have died.
Put into context, the regular seasonal flu kills about 36,000 people nationwide every year. But it usually hits older people harder than young people -- whereas the opposite holds true for swine flu.
To help prevent a surge of sick students, teachers and others, clinical trials for a vaccination are starting this month, expected to be followed by a voluntary vaccine program.
Those vaccinations were initially anticipated to begin mid-October, but last week health officials expressed some concern about whether that timeline will hold. Data from the trials may not be ready for scientists to review until the end of September, and it could take another four to six weeks to begin a vaccination program. That could mean the start of the vaccine program gets pushed back into November -- months after the start of school.
Last week, the Government Accountability Office (GAO) issued the latest in a series of warnings saying "gaps remain at all levels of government" when it comes to planning for a possible pandemic flu.
"Further actions are needed to address the capacity to respond to and recover from an influenza pandemic, which will require additional capacity in patient treatment space, and the acquisition and distribution of medical and other critical supplies, such as antiviral and vaccines," the GAO report said.
School are nonetheless trying to prepare for what could lie ahead.
"I think there's more of an awareness going into this school year," Ball said. "We certainly know that we have a lot of preparation to do and a lot of planning to do."
Coburn said, "We just want to make sure that kids are washing their hands along with parents and staff, and that we work together, as far as public health, parents, and school communities to make sure that children take preventative actions."
Ball has basic tips: "When you don't feel good, stay home. If you have a temperature, stay home. Don't participate in your sports when you're running a fever."
"The early days of the H1N1 outbreak have passed," said Schaffner. "Over 1 million cases have occurred in the U. S., and the virus now is well-embedded in our communities. School closings can no longer be seen as an effective means of limiting transmission."
ABC News' Olivia Hallihan, Courtney Hutchison and Dan Childs contributed to this report.