This is a multicenter, randomised, four arms placebo controlled study to evaluate the safety and tolerability of 10 mg inhaled zanamivir once a day and 75 mg oseltamivir capsule orally once a day relative to placebo over 16 weeks (112 days). Enrolled subjects will be randomly assigned to 2:1:2:1 ratio (active oseltamivir: placebo: active zanamivir: placebo) on one of the four study treatment groups.

It is hypothesized that oseltamivir and zanamivir will protect participants from becoming infected with influenza.

We plan to recruit 130 non-pregnant subjects including Health Care Workers, which refer to anyone who works in the hospital, into each active arm and 65 healthy, non-pregnant subjects including Health Care Workers into each placebo arm for a total of 390 study subjects from 4 study sites in Bangkok and Nonthaburi province, Thailand: (i) Faculty of Medicine Siriraj Hospital, (ii) Bamrasnaradura Infectious Diseases Institute, (iii) Chest Disease Institute, and (iv) Hospital for Tropical Diseases.

Randomisation Groups:

Zanamivir for inhalation, (5 mg per inhalation), two inhalations, once daily using a ROTADISK/DISKHALER for 112 days. The dose should be administered at approximately the same time each day.

Placebo (lactose powder), two inhalations, once daily using a ROTADISK/ DISKHALER for 112 days. The dose should be administered at approximately the same time each day.

Oseltamivir capsules (75 mg per capsule), one capsule daily by mouth (PO) for 112 days. The dose should be administered at approximately the same time each day.

Placebo capsules, one capsule daily for 112 days. The capsule should be administered at approximately the same time each day.

Study duration

The study is expected to last up to about 12 months. The study will consist of:

• a screening visit
• 10 study visits: Days 0 , 7 (+2), 14 (+2), 28 (+2), 42 (+2), 56 (+2), 70 (+2), 84 (+2), 98 (+2) and 112 (+2) and
• One follow-up visit on Day 120 (+2)

Inclusion Criteria:

• A subject will be eligible for inclusion in this study only if all of the following criteria apply:

  1. Healthy male or female aged 20 - 65 years. Healthy determined by the Investigator based on medical history and screening examinations.

  2. Read and understand study related materials intended for subject.

  3. Signed informed consent prior to study participation.

  4. Willingness and ability to comply with the study protocol for the duration of the trial.

  5. Female subject who is of reproductive potential agrees to use an acceptable method of birth control (e.g., intrauterine device, abstinence or hormonal contraceptive drug) throughout the study (D120+2).

  6. For male subject, he must agree to use an acceptable method of birth control (e.g. abstinence or condom) throughout the study (D120+2).

     Exclusion Criteria:

• A subject will not be eligible for inclusion in this study if any of the following apply:

  1. Females who are pregnant, trying to get pregnant or are lactating.
  2. Current or a history of asthma or chronic obstructive pulmonary disease within the last 5 years.
  3. Abnormal pulmonary function test according to The Thoracic Society of Thailand Guidelines for Pulmonary Function Tests: (i) FVC < 80% of the predicted value for age and sex or (ii) FEV1/FVC <70%. (see Appendix 2)
  4. Any other chronic or acute diseases requiring treatment.
  5. An abnormal ECG indicating disease that requires immediate investigation or treatment
  6. An abnormal chest x-ray indicating an active disease process.
  7. A creatinine clearance < 30 mL/min as determined by Cockcroft-Gault equation (see below)
  8. AST or ALT ≥ 1.5 x ULN
  9. Use of a live attenuated influenza vaccine or any anti-influenza drug within 14 days prior to the first dose of study drugs/placebos.
  10. History of alcohol or substance abuse or dependence which in the opinion of the investigator would interfere with subject compliance or safety
  11. Subjects who have a history of allergy to the study drug or drugs of the same class, or a history of severe drug (e.g. toxic epidermal necrolysis) or other allergy (e.g. previous history of anaphylaxis) that, in the opinion of the investigator, contraindicates participation in the trial.
  12. The subject has participated in a clinical trial and has received investigational drugs within 60 days prior to the first dose of study drug.
  13. Subjects who, in the opinion of the investigator, are unlikely to comply fully with study procedures.
  14. History of any mental illness requiring hospitalisation or outpatient psychiatric treatment within the last 12 months
  15. Any suicidal attempt within the previous 5 years.
  16. Screening HADS anxiety or depression score > 8.
  17. Hemoglobin <11g/dL or neutropenia of < 1000 per microlitre or a platelet count of less than 100,000 cells/mm3 Cockroft formula: CrCl (mL/min) = (140 - age) x Wt / 72 x serum creatinine (females x 0.85), age in years, Wt in kg, serum creatinine in mg/dL.