Abstract
Concerns that a new influenza strain may arise that would exhibit similar properties to the 1918–1919 pandemic virus prompted the decision in 1947 to establish a World Health Organization global program for influenza surveillance. This program has contributed greatly to understanding of the epidemiology of influenza and provides the basis for the timely updating of influenza vaccine formulations during interpandemic periods. The spread of pandemic influenza, however, is extremely rapid and, in 1957 and 1969, occurred before sufficient supplies of vaccine could be prepared and administered. Recent evidence regarding the origin of new influenza strains provides some opportunities for improving surveillance for pandemic influenza, but there is a danger that the benefits may be offset by even more rapid spread of a future pandemic due to changes in worldwide transportation and commerce.