Each year, over 20% of the human population is infected with the influenza virus, resulting in 250,000–500,000 related deaths globally and ~38,000 deaths in the United States alone. Of further concern is the potential for pandemic outbreaks, which pose a severe worldwide threat to public health (1, 2). Vaccination has proven to be a critical tool for controlling the spread of infectious diseases, as evidenced by the eradication of polio, smallpox, and diphtheria in most parts of the world. Influenza…