Introduction In 1918-19 approximately 50 million deaths were due to the Spanish H1N1 virus pandemic; a respiratory virus. According to the World Health Organization, the second influenza A H1N1 pandemic in 2009 spread to more than 200 countries causing more than 18,000 deaths. Before the World Health Organization announced the official end of the pandemic in August 2010, the World Health Organization issued a phase 6 warning in July 2009 that H1N1 could soon become a global pandemic. It is important to recognize that the 2 different epidemics had different A/H1N1 strains affecting the global population; this suggests that A/H1N1 has a high capacity for mutation, severely complicating the human body's natural antigenic drift immune mechanism. (Qi-Shi Du et al., 2010) Epidemiology According to the swine influenza investigation team of April 15 and 17, 2009, the new influenza A (H1N1) virus of swine origin (S-OIV) was isolated from two epidemiologically unrelated patients in the United States. The same strain has been identified in other countries such as Mexico and Canada. In the United States, 60% of patients were 18 years old or younger, suggesting that the younger population was more susceptible to S-OIV transmission or the possibility that the older population had developed a small amount of antibodies from the S-OIV vaccine. 1976 swine flu (H1N1). Eighteen percent of patients had recently traveled to Mexico, and 16% were identified due to school outbreaks. (France, Jackson & Schrag, 2010) The most common presenting symptoms were fever (94% of patients), cough (92%) and sore throat (66%); Twenty-five percent of patients had diarrhea and 25% had vomiting. Therefore, the criteria characterizing S-OIV infection are comparable to the…… middle of the paper…… SM, My Yang, Halvorson, DA & Sreevatsan, S. (2009) The Feasibility of Using HighResolution Genome Sequencing of Viruses influenza A to detect mixed and quasispecies infections. PLoS One 4(9), 7105.Thorlund K, Awad T, Boivin G, Thabane L. Systematic review of influenza resistance to neuraminidase inhibitors. BMC Infect Dis 2011;11:134.Vries, EVD, Schutten, M & Boucher, CAB (2010) The potential of multidrug-resistant influenza. New England Journal of Medicine 24, 599–604. Writing Committee of the WHO Consultation on Clinical Aspects of Pandemic Influenza (H1N1) 2009. (2009) Medical Progress Clinical Aspects of Pandemic 2009 Influenza A (H1N1) Virus InfectionGambaryan A. S & Matrosovich MN(1992) A test in progress solid with enzymatic linkage for influenza virus receptor binding activity. Journal of Virology 39, 111–123.