The aim of this review is to describe the detrimental impact influenza virus has on an individual as well as on the community and to reinforce the strategies of prevention and treatment of this disease. The influenza viruses are capable of causing annual epidemics because of the constant changes that occur at the antigenic sites of the surface proteins. These antigenic changes, also known as antigenic drift (minor change) and antigenic shift (major change), allow the influenza virus to infect a substantial segment of the population with incomplete or no immunity. Composition of the influenza virus vaccine is changed on a yearly basis to provide the best match to new influenza virus strain(s) predicted to cause the next epidemic. Only by annual administration of influenza virus vaccine prior to the epidemic can health care providers expect to prevent influenza virus pneumonia and its associated complications in high-risk groups. Recent studies have demonstrated the medical prudence and cost effectiveness of preventing influenza virus infections in high-risk groups who are most susceptible to the complications of the influenza virus.