On April 26, 2009, the U.S. Department of Health and Human Services (HHS) declared a public health emergency for 2009 pandemic influenza A (H1N1) (hereafter, pH1N1).1,2
Influenza activity remained at higher-than-normal levels throughout the spring and summer, peaking in late October and early November 2009, and disproportionately affected younger people.3
The pH1N1 influenza virus was determined to be susceptible to the neuraminidase inhibitors (oseltamivir and zanamivir), which were recommended for treatment and chemoprophylaxis of pH1N1 infection.4
Given the pandemic spread and potential severity of infection with the pH1N1 virus, the Centers for Disease Control and Prevention (CDC) requested an Emergency Use Authorization to expand neuraminidase inhibitor use to include children younger than one year of age (oseltamivir) and patients of any age with severe disease (oseltamivir and zanamivir).5
Adverse events from medications are typically monitored through passive surveillance, primarily the U.S. Food and Drug Administration Adverse Event Reporting System (AERS), which relies on voluntary reporting of adverse drug events (ADEs) by health-care professionals and consumers and reporting by pharmaceutical manufacturers.6
Because the early stages of a novel influenza pandemic are associated with many unknowns, including possible delays in availability of vaccine, a 2008 Institute of Medicine report recommended that HHS consider options, in addition to AERS, for capturing antiviral adverse events, as use of antivirals, particularly among vulnerable populations, is likely to increase.7
We used data from an active, population-based surveillance system to monitor emergency department (ED) visits for antiviral ADEs during pH1N1 and compared these data with those from previous influenza seasons.