GP-681

Main study objectives: To evaluate the effectiveness of a single oral dose of GP681 tablets compared with placebo in the prevention of influenza exposure in family members (household contacts) of influenza patients (index cases). Secondary study objectives: 1) To evaluate the effectiveness of a single oral dose of GP681 tablets compared with placebo in the prevention of influenza exposure in household contacts through other secondary endpoints; 2) To evaluate the safety of a single oral dose of GP681 tablets compared with placebo in the prevention of influenza exposure in household contacts.