"The purpose of these trials is always to make sure they are safe, " said Dr. Karen Kotloff, professor of pediatrics and lead investigator and researcher at Maryland's Center for Vaccine Development.

CNN: School: No shortage of volunteers for swine flu vaccine trials

"This virus has the potential to cause significant illness with hospitalizations and deaths during the U.S. flu season this fall and winter, " said Dr. Karen Kotloff, professor of pediatrics and lead investigator and researcher at Maryland's Center for Vaccine Development.

CNN: U.S. trials for H1N1 vaccine announced

Even if teens have not actually engaged in risky behaviors but merely brag about them online, this can still affect their future behavior, said study co-author Dr. Dimitri Christakis, professor of pediatrics at the University of Washington and director of the Center for Child Health, Behavior and Development at Seattle Children's Hospital.

CNN: Study: Teens on MySpace mention sex, violence