Spanish influenza epidemic of 1918 was truly a world-shaking event. The numbers of dead are estimated to be somewhere between 50 and 100 million people, and it is estimated that the numbers of those who were infected and survived may have reached as high as five to ten times the number of dead. Almost one in three human beings alive in 1918 would be infected by the virus. But in particular, the epidemic had a number of longer lasting effects on the history of America, which it is worth examining in closer detail. From a scientific standpoint, the Spanish influenza was nothing remarkable: it followed the standard path of an influenza virus, in making the leap from an animal host population into infecting humans. The best contemporary efforts to reconstruct the disease's origin suspect that it either leapt directly from birds to humans, or else the avian flu transmitted to swine first, and thereafter to humans. In any case, its origins and methods of transmission were no different in basic features from earlier and later influenza epidemics: the chief difference was the ability of the Spanish Flu to involve pneumonia, making it particularly fatal. Yet the largest historical irony of the epidemic, as noted by Crosby, is that the Spanish influenza pandemic came at a time when medical science had been making huge advances...

Crosby gives the details of medical progress unto that point:
Remedies for, or vaccines against, or, at least, methods of limiting the spread of smallpox, typhoid, malaria, yellow fever, cholera and diphtheria had been devised and proven successful….Welch's superior, Army Surgeon General William Crawford Gorgas, had led the forces that controlled and almost eliminated the scourge of the Caribbean, yellow fever, from Cuba and the Panama Canal Zone. Yet these doctors now stood nearly as helpless in the presence of this epidemic of Spanish influenza as Hippocrates and Galen in the presence of epidemics of their time. Welch, Vaughan, Cole, and all the physicians of 1918 were participants in the greatest failure of medical science in the twentieth century or, if absolute numbers of dead are the measure, of all time. (Crosby 10).

As Crosby's invocation of the U.S. Army's attempts to contain and control the disease -- it had, after all, infected U.S. "doughboys" who had been sent en masse to France to fight in World War I -- will remind us that the U.S. Army was perhaps the only governmental organization capable at the time of dealing with a public health crisis. Barry has noted in particular that the increased immigration and urbanization of…