This review aims to answer the following questions:
1. How effective is zanamivir in shortening the time-course, reducing the severity of illness or preventing death in otherwise healthy adults with influenza?
2. How effective is zanamivir in shortening the time-course, reducing the severity of illness or preventing death in adults at risk of suffering severe adverse outcomes from influenza?
3. What is the frequency and severity of adverse effects associated with the use of zanamivir in both healthy and at-risk adults?
4. What is the cost-effectiveness of zanamivir for the treatment of influenza in healthy and at-risk adults?