Influenza pandemics in perspective.

IT IS NOW nine months * since the recognition of an influenza epidemic caused by swine influenza virus in military personnel at Fort Dix, NJ. The gestation period of an influenza pandemic is unknown, but in this case, long labor has preceded the delivery. Whatever else may be said of our unprecedented national effort for the amelioration of a pandemic for the first time in history, we now have an overwhelming balance of vaccine doses available to manifest cases of disease—about 150 million to zero (sporadic cases occurred subsequently in January). The basis of the decision to act aggressively against swine influenza has been cited more frequently in the lay press than in professional journals. In brief, the decision rested on (1) expectation of the emergence of a new major virus variant within the next few years on the basis of decennial periodicity of pandemics, 1 (2) the unprecedented observation of