Randomly selected Harvard undergraduates and their friends will report their popularity and flu-like symptoms as participants in a new Harvard Medical School study seeking to explain how social networks affect the spread of diseases.

“By looking both at whether you’ve had the flu and where you are in the social network, we think you can get an early warning of an epidemic,” said HMS professor and Pforzheimer House Master Nicholas A. Christakis, who is conducting the study.

Christakis added that he did not want to reveal the details of his hypothesis for fear of potentially corrupting the results of the study. But he said that if there is no H1N1 epidemic, his “experiment will be a flop.”

Last Friday, Christakis sent e-mails to 650 randomly selected undergraduates, asking them to sign up to self-report their flu symptoms twice a week for 12 consecutive weeks. The participating students were also asked to nominate two to three friends, who will be asked to take part in the study as well.

When the study’s participants first sign up, they are also asked questions about how popular they are.

In exchange for participating in the study, the students will receive a $5 gift card to JP Licks every other week while the study is in progress.

“If this works, we’ll have invented a new method for attacking diseases, which could have broad relevance far outside Harvard,” Christakis said.

He added that he hopes that at least 75 percent of the students he e-mailed enroll in the confidential study. He said that the study will not report sick students to University Health Services.

Since the study may signal an early warning for a potential H1N1 epidemic, Christakis said he has garnered support from both the College and UHS.

“I think it’s a rather unique study,” UHS Director David S. Rosenthal ’59 said. “It will be a fascinating work.”

—Staff writer Danielle J. Kolin can be reached at dkolin@fas.harvard.edu.