A history of influenza

From the history of influenza epidemics and pandemics, which can be traced back with some accuracy for the past three hundred years, and with less certainty before this time, it is apparent that outbreaks occur somewhere in the world in most years. Annual epidemics are due to antigenic drift; and pandemics, occurring at 10 to 50 years intervals, are due to new virus subtypes resulting from virus reassortment. Nothing has been introduced during the past 100 years to affect the recurrent pattern of epidemics and pandemics; and our future in the new century is clearly indicated by our past. This past experience is reviewed in the present paper.