Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease at the National Institutes of Health, told ABC News the government hopes to enroll about 2,500 volunteers in the trials -- including about 1,200 children between the ages of 6 months and 17 years old.
Fauci said trials will begin in the first or second week of August -- first on adult volunteers and then on children.
"Before you put anything into a child, you really need to know some preliminary safety data in adults," Fauci said Wednesday. "We're not talking about safety data measured over months and months. We're talking about two days to a week-and-a-half. If that looks clear, then we will move on to the children."
Vaccine development has proven difficult. The virus grows slowly and there's always concern about rare but dangerous side effects with a new vaccine that's being rushed into production.
It will take about six weeks to get results back from all of the clinical trials.
This week, tests began on a vaccine in Australia. Adelaide, Australia-based Vaxine Pty Ltd. and Melbourne-based CSL Biotherapies injected the first adult volunteers this week in separate trials starting days apart.
There's also concern about how hospitals and schools will handle an onslaught of H1N1 cases that could overwhelm the health system and force school closures.
Hospitals have plans in place to prep for a surge of patients coming through the doors and the possibility of doctors and nurses falling ill.
At Children's National Medical Center in Washington, D.C., health workers have ordered additional masks, respirators and anti-flu medication. They have plans to double up patients if need be, and put cots in public areas.
"By all means, we need to be very concerned about the possibility that this is gonna come back in a big way," Holbrook said.
Schools also have "what if" plans in place in case teachers -- as well as students -- are too sick to come to work.
Some of the preparedness plans readied in 2006 to battle a potential outbreak of bird flu are now being dusted off and updated for swine flu.
But Dan Domenech, executive director of the American Association of School Administrators, a group that represents 14,000 school administrators around the country, said most schools are in the dark about when to make the call and how long to keep kids home.
Domenech clarified that local school boards will always make the call about whether to close schools due to an outbreak.
But he also added Wednesday, "We'd like to have a uniform set of criteria to understand what schools should look for. This is a national issue. It's being dealt with nationally. We should all be looking at the same set of guidelines."
"I think the public, in terms of preparation, ought to think of their own personal plans," Rehm said. "What if the schools were closed? What about work? Can we work distantly? Telecommuting might be not the exception but the rule."
Med Page Today's Todd Neale contributed to this report.