In June 2009, the World Health Organization (WHO) declared a global pandemic of influenza A (H1N1). Although little is known about the pandemic influenza strain in children, during previous pandemics and influenza seasons children less than one year of age were shown to be at higher risk of influenza complications than older children. In light of the 2009 H1N1 pandemic situation, the U.S. Food and Drug Administration (FDA), European Medicines Agency (EMA), and Health Canada issued emergency authorizations for oseltamivir to be used to treat and prevent influenza in infants under 1 year of age. It is anticipated that oseltamivir use in infants will dramatically increase due to the new authorizations for use in this population and high prevalence of H1N1 influenza circulating in the population. Ongoing safety surveillance is critical and this study will provide further data for evaluating the risk/benefit ratio of prescribing oseltamivir to this population in the current milieu of both seasonal and pandemic influenza viruses circulating in the population. The study will also provide useful information on the dose and duration of treatment used in clinical practice and their relationship to adverse events.

This study is a prospective, observational, multicenter short-term safety study of the use of oseltamivir (prophylaxis or treatment) in children 24 months of age or younger. An internal comparator group of children diagnosed with influenza and not treated with antiviral medications will be enrolled. The study includes a 30-day follow-up period and will be conducted in multiple sites in multiple countries within the European Union. The study will cover two consecutive influenza seasons: 01 October 2009 - 31 May 2010 and 01 October 2010 - 31 May 2011. Data collection may be interrupted in the interim period between influenza seasons (June 1, 2010 - September 30, 2010), depending on whether the influenza season follows the expected cycle.

Inclusion Criteria:

• 24 months of age or younger at time of enrollment
• Diagnosis of influenza A or B (suspected* or confirmed by viral testing) either treated with oseltamivir or with no antivirals OR prescribed oseltamivir for post-exposure influenza prophylaxis
• Parent/legal guardian willing to provide informed consent and be contacted by telephone as part of follow-up

Exclusion Criteria:

• Patients will be excluded if treated with an influenza antiviral other than oseltamivir, including amantadine, rimantadine, or zanamivir.

  • Suspected influenza is defined as an acute febrile illness characterized by the presence of fever and 1 or more of the following symptoms: cough, coryza/nasal congestion or sore throat.

The study will be conducted in multiple sites in multiple countries within the European Union. Initially, five countries (United Kingdom, Austria, Finland, Poland, Germany) are selected for inclusion, but additional countries in Europe, are likely to be added. It is estimated that 3-12 sites per country will be enrolled, with a target of at least 900 patients. If additional countries are added, the number of sites/patients recruited per country will be adjusted accordingly.