Researchers are in a race against time, as they try to figure out through vaccine trials what the most effective H1N1 vaccine is before flu season begins.
"The clock is ticking and when children go back to school, children are going to be very susceptible to this virus," said University of Maryland professor of pediatrics Dr. Karen Kotloff, who is a lead investigator for the clinical trials .
In eight hospitals from coast to coast, volunteers will receive a series of shots, some stronger than others to figure out how much vaccine, and how many shots, it will take to protect the public.
Volunteers will get two shots, three weeks apart, while researchers look at the swine flu vaccine's safety, effectiveness, and whether it will take one dose or two to provide immunity.
"We'll collect a blood specimen at every visit to measure the antibodies to the vaccine," explained Dr. Lisa Jackson, the researcher leading the trials at Group Health Cooperative in Seattle.
Volunteers like Paul Ritterhoss will be closely monitored for the next several weeks. While doctors say the process is safe, Ritterhoss and others risk fever, allergic reactions and a remote chance of paralysis and even death.
"The opportunity to contribute to something that is really on the cutting edge of science, that has significance to lots of people around the world, is something that makes the risk worth it," Ritterhoss said.
Fellow vaccine volunteer Cynthia Thomsen said she was not worried, either.
"I trust what they are doing and I think it is great what they are doing. I think you need to do things like this to benefit others," Thomsen said.
Most trials begin this week, and involve 2,500 paid volunteers in all -- half adults, half children.
Researchers will see how adults tolerate the vaccine before they begin trials in children, to test for any adverse side effects.
Elizabeth Depooter's 4-year-old son Dane will take part as a child volunteer.
"It concerns me a little bit, but I feel like it's pretty safe. I just feel like it's very important to be part of something bigger than us and to participate in studies like this," Depooter said.
Vaccine companies are also running their own trials.
The hope is that the vaccine will be ready to go in October, before the winter sets in. Doctors say they believe when the temperature drops, the pandemic will take off.
ABC News' Lisa Stark contributed to this report.