The mechanisms underlying influenza-related mortality remain controversial. Progressive pneumonia following an insufficient antiviral host response is one possible cause [9] . Virally-induced excessive and/or dysregulated lung inflammation is another potential mechanism [10, 11, 12, 13] . Secondary bacterial infections have also been proposed as the primary contributors to influenzarelated mortality, due to virally-injured epithelium or virusattenuated leukocyte responses [13, 14, 15] .