The government is asking thousands of men, women and children to agree to test out the first swine flu shots. The tests will help determine whether people should be given one shot or two and also will consider the optimal time for shots to be administered.
As the United States readies for a potential fall surge of the virus, today an advisory committee to the Food and Drug Administration is meeting to further discuss the clinical trials for potential vaccines.
The meeting is happening as Homeland Security Secretary Janet Napolitano, Health and Human Services Secretary Kathleen Sebelius and Secretary of Education Arne Duncan brief members of Congress about the state of the H1N1 swine flu pandemic.
On Wednesday, the government announced eight medical centers where testing will take place, likely next month.
Meantime, the virus continues in the United States. Flu viruses typically disappear in warm weather, but this year, swine flu has swept through camps and summer schools. At the U.S. Coast Guard Academy in Connecticut, dozens of cadets are ill.
"It certainly isn't over," said Will Humble, interim director of the Arizona Department of Health Services. "And in fact, my whole career in public health, over 20 years, I've never seen flu circulating in the middle of the summer. None of my staff has seen it. Public health hasn't ever seen what is happening right now."
Swine flu is expected to spread rapidly in the U.S. once the fall flu season gets under way just as kids go back to school, the same time that germs typically spread more rapidly.
So what do public health officials anticipate for the season ahead?
"Best case: The vaccine would be in early, all of us would be vaccinated, and when H1N1 comes along we will have mitigated its impact," said Dr. William Schaffner, chairman of Vanderbilt University Medical Center's department of preventive medicine.
Ideally, Schaffner said, vaccinations would begin in mid-October.
But infectious disease experts also pointed out the possibility of a much worse outcome.
"A worst case scenario would be more like the 1918-1919 pandemic," said Dr. Susan Rehm, vice chair of the department of infectious disease and executive director of physician health at the Cleveland Clinic. "We prepare for the worst and hope for the best."
Dr. Peter Holbrook, chief medical officer at Children's National Medical Center in Washington, D.C., told ABC News Wednesday that a worst case scenario also could mean, "Somewhere along the line [the virus] mutates and becomes a much more severe virus."
A key weapon in the battle to keep people healthy will be a swine flu vaccine.
Clinical trials in the U.S. will be conducted at eight medical centers -- Vanderbilt University in Nashville, Emory University in Atlanta, University of Iowa in Iowa City, Children's Hospital Medical Center in Cincinnati, University of Maryland School of Medicine in Baltimore, Saint Louis University in St. Louis, Baylor College of Medicine in Houston and Group Health Cooperative in Seattle.