Any patient over 1 year of age who presents to a participating institution with confirmed influenza A and who meets the study inclusion/exclusion criteria may be approached for informed consent. Choice of antiviral is up to the study physician. Children aged 1-6 years and asthmatics should receive oseltamivir. The weight- and age-adjusted dosage used will be that approved for treatment of uncomplicated seasonal influenza, and doses will be administered twice daily for 5 days for patients with normal renal function. All patients who are clinical and/or virologic failures at day 5 will be treated for an additional 5 days of antivirals. After coming off antiviral therapy patients can be discharged at day 10 if deemed ready by study physicians and they are virologically negative.