Philadelphia's epidemic had one peak and, therefore, dramatic unity and something of the quality of tragedy. San Francisco's epidemic had two climaxes, the second of which was, of course, the antithesis of dramatic unity, an anticlimax. San Francisco's epidemic was, perforce, a macabre comedy.

In 1918 San Francisco had a population of 550,000, less than one-third that of Philadelphia, but there were important similarities between the two populations. San Francisco, too, was the beneficiary and victim of recent and rapid growth. The population had grown by one-fifth since 1914, and many of the newcomers had arrived very recently to take jobs created by the war. It, too, was crowded with immigrants of foreign birth, about 130,000 adults and uncounted children. Many of the immigrants were Italian, despite the fact that a continent as well as an ocean separated them from their motherland. Many others were Chinese, separated from the leaders of the city's government and society by an especially deep linguistic and cultural chasm, although San Francisco's Chinatown was many decades old.

San Francisco had one enormous advantage vis-à-vis the pandemic: a full and clear warning of what was coming. The story of Spanish influenza in Boston and Camp Devens was available to its leaders days before the first death was credited to the disease in San Francisco. Congress voted its one-million-dollar appropriation to fight flu in September before the disease had more than a toehold in the San Francisco Bay area.