Experimental and clinical studies in adults have reported that green tea catechins prevent influenza infection. In this clinical randomized study, the investigators aimed to determine the effects of gargling with green tea on the prophylaxis of influenza infection among high school teenagers.

Influenza infection is the principal cause of acute respiratory illnesses and occurs in epidemic or pandemic worldwide. It spreads easily among high school students and from them to the rest of the community; therefore the prevention of influenza is very important.

Experimental studies have revealed that some components of green tea can prevent influenza infection in vitro. In clinically, gargling with green tea catechins has been reported to have possibilities to preventing influenza infection in adults; however, little clinical evidence in teenagers has so far been existed. Based on this background, the investigators designed a randomized study to evaluate the clinical efficacy of gargling with green tea in preventing influenza infection among high school students.

Inclusion Criteria:

• aged from 15 to 20 years
• obtained written informed consent from both the student and parent before participation
• possible to gargle during 90 days
• possible to fill in questionnaire

Exclusion Criteria:

• Possessing allergy to green tea
• Possessing history of influenza infection within 6 months before entering the study
• Possessing severe immune disease or whole body infection
• severe cardiac, respiratory, renal, or hepatic dysfunction
• diagnosed as inadequate to participate in the study by student doctor