Seasonal H1N1 Nonstructural Protein 1 Antibody: Influenza A virus is a major public health threat, killing more than 30, 000 people per year in the USA. In early 2009, a novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in specimens obtained from patients in Mexico and the United States. One of the less studied proteins encoded by, but not incorporated in, the influenza virus is the nonstructural protein (NS) 1. NS1 counters cellular antiviral activities and acts as a virulence factor. It can bind to double-stranded RNA and sequester it from 2'-5'OAS, preventing the activation of the RNAse L, which normally acts to degrade RNA and prevent virus replication. NS1 also binds to and inhibits the anti-viral protein kinase PKR.