Interferon-induced transmembrane protein 3 (IFITM3) is a protein that in humans is encoded by the IFITM3 gene. [5] [6] [7] It plays a critical role in the immune system's defense against Swine Flu, where heightened levels of IFITM3 keep viral levels low, and the removal of IFITM3 allows the virus to multiply unchecked. [8] This observation has been further advanced by a recent study from Paul Kellam's lab that shows that a single nucleotide polymorphism in the human IFITM3 gene purported to increase influenza susceptibility is overrepresented in people hospitalised with pandemic H1N1. [9] The prevalence of this mutation is thought to be approximately 1/400 in European populations. [9] [10]