Influenza pandemics

Influenza is associated with high morbidity and mortality and is caused by influenza viruses. These viruses are characterized by a high rate of evolution, either through point mutations or the exchange of genetic segments. Influenza A viruses with a new genetic composition due to one or more reassortment events, with antigenic characteristics to which the human population is susceptible and with the capacity for efficient human-to-human transmission, can be considered viruses with pandemic potential. Since 1918, there have been four pandemics caused by different influenza viruses, with varying degrees of transmissibility and severity, sometimes strongly influenced by environmental factors in addition to viral characteristics. Given that all pandemic viruses have been of zoonotic origin, it is imperative to work towards global surveillance in animals, humans and the natural environment for their early detection.