As late as 1900, it was more difficult to get into a respectable American college than into an American medical school.

From The Great Influenza: The Story of the Deadliest Pandemic in History by John M. Barry.  

The story, however, begins earlier. Before medicine could confront this disease with any promise of effect, it had to become scientific. It had to be revolutionized.

Medicine is not yet and may never be fully a science (the idiosyncrasies, physical and otherwise, of individual patients and doctors may prevent that) but, up to a few decades before World War I, the practice of medicine had remained quite literally almost unchanged from the time of Hippocrates more than two thousand years earlier. Then, in Europe first, medical science changed and, finally, the practice of medicine changed.

But even after European medicine changed, medicine in the United States did not. In research and education especially, American medicine lagged far behind, and that made practice lag as well.

While for decades European medical schools had, for example, required students to have a solid background in chemistry, biology, and other sciences, as late as 1900, it was more difficult to get into a respectable American college than into an American medical school. At least one hundred U.S. medical schools would accept any man (but not woman) willing to pay tuition; at most 20 percent of the schools required even a high school diploma “ for admission (much less any academic training in science) and only a single medical school required its students to have a college degree. Nor, once students entered, did American schools necessarily make up for any lack of scientific background. Many schools bestowed a medical degree upon students who simply attended lectures and passed examinations; in some, students could fail several courses, never touch a single patient, and still get a medical degree.

Not until late (very late) in the nineteenth century, did a virtual handful of leaders of American medical science begin to plan a revolution that transformed American medicine from the most backward in the developed world into the best in the world.