We also know that every wave of every pandemic has been at least a little different. In 1918, of course, that difference was dramatic, but 1968 may be more puzzling. In the United States, 70 percent of pandemic deaths occurred in the 1968–69 influenza season, with the rest in 1969–70. Europe and Asia were the opposite, with few deaths in 1968–69 and the overwhelming majority in 1969–70—even though a vaccine was available by then. Incidentally, the 1968 pandemic gave us the H3N2 virus, which has continued to cause the most severe disease of several circulating influenza viruses ever since.
