Let us examine the course of the pandemic in two cities, on the East Coast, Philadelphia, which had a one-wave epidemic; and on the West Coast, San Francisco, which had two waves. Philadelphia had the most severe experience of any major American city, and San Francisco had the worst trial of any West Coast city, but their travail was only slightly worse than that of many other cities and its chief aspects were common to nearly every city in the nation.

The federal estimate of the population of Philadelphia in 1918 was 1,700,000, but the city's Department of Public Health and Charities insisted that war industry had added another 300,000. Nearly every home had lodgers, except those in the well-to-do sections. Philadelphia's Quaker traditions were fraying under the pressure of expanding ghettos. Growing up alongside the black ghetto, one of the oldest and largest in the North, were neighborhoods of nearly every oppressed nationality and ethnic group of Europe. As of the 1920 census 361,000 Philadelphians were adults of foreign birth, and that number did not include anyone under 21 born outside the United States, of whom there must have been many thousands. When the city's Bureau of Health published mortality tables for the year of the flu pandemic, it included categories for people born in the United States, Canada, England and Wales, Scotland, Ireland, Sweden and Norway, France, Germany, Austria-Hungary, Italy, Poland, Russia, Rumania, and China.

If forewarned had really meant forearmed in 1918, then Philadelphia would have come through the pandemic with little damage.