Influenza is a viral, pandemic and respiratory disease with high morbidity particular and significant mortality rate amongst humans. WHO has counted that each outbreak of epidemic is costing between 10–60 million dollars to one million citizens and each year there are between 250.000 to 500.000 deaths caused by flu. Eight RNA segments of influenza A and B viruses and seven segments of the C viruses are independently encapsulated by viral nucleoprotein. The heamagglutinin is the most important protein of the influenza virus. All antigenic HA and NA subtypes of influenza A viruses are derived from birds. The pig trachea is the only known tissue that contains receptors for avian and human influenza viruses. Influenza occurs in two forms: pandemic and epidemic. Local symptoms such as pharyngitis, coughing, sneezing, discharge, are result from the direct action of the virus, or destruction of billions of cells of the respiratory epithelium. Systemic signs such as fever, malaise, myalgia, chilliness, headaches, occur because of induced and increased levels of cytokines by the virus. Vaccine is the best prevention against influenza. Immunity is achieved after two weeks of vaccination.