Influenza is a virus that exhibits a complex seasonal pattern of circulation. The World Health Organization (WHO) tracks evolving influenza viruses infecting humans, through the global influenza surveillance network. However, tracking influenza viruses is difficult due to their characteristics, most notably their ability to evolve quickly and their ability to infect avian and other mammalian species. The mortality and morbidity rates based on worldwide influenza epidemics are briefly reviewed, as well as the impact of influenza on the elderly population. There are four WHO collaborating centers for influenza (CCIs) located in London, Atlanta, Melbourne, and Tokyo and 110 national influenza centers (NICs) worldwide. Active NICs isolate and identify influenza viruses and send the isolated viruses to CCIs for analysis. The purpose is to detect a variant strain that could lead to a new epidemic. The CCIs are responsible for providing data for the influenza vaccine recommendations that WHO issues to the world twice a year. There are a number of limiting factors faced by WHO collaborating centers affecting both vaccine strain selection and special investigations. In addition, limiting factors are identified for generating data for influenza vaccine strain selection. Influenza surveillance is not seen as uniform throughout the world indicating a need to establish influenza surveillance or increase the number of influenza viruses that are isolated. CCIs need to increase their capacity to grow, store, and analyze influenza strains and develop improved methods to handle increased influenza viruses at critical times. Automation is seen as greatly increasing the number of influenza isolates and serum specimens. Increased data would be beneficial in expanding the knowledge of the epidemiology, ecology, evolution, and pathogenesis of influenza viruses and vaccine strain selection.