Again West, in the same year wrote, “From our present experience we must conclude that influenza is infectious in a very high degree indeed, and that the protection afforded by an attack is imperfect, or of very short duration. Indeed, one attack seems actually to predispose, after a time to another, or, to put it differently, that the positive phase of protection is followed by a negative phase, in which the individual seems rather more than less liable to succumb to infection if exposed to it. It seems more likely that an individual may never have influenza at all than that, having had it once, he should never have it again. Some, indeed, seem to offer so little resistance that they develop it regularly once or twice a year.” We have previously shown that the relatively low morbidity among the older age groups in 1918 is not satisfactorily explained by an immunity lasting over from the epidemic of 1889–93. If such were the case the change in mortality rate in large groups of individuals would occur at the age of 30. During the autumn of 1918 many observations were made, particularly in the armies, of light incidence in those groups or communities that had had the disease in mild form in the spring of the same year. Parsons quotes many similar observations for the period 1890–1893. V. C. Vaughan relates that at Camp Shelby, Mississippi, “there was in April a division of troops numbering about 26,000. An epidemic of mild influenza struck this camp in April, 1918, and within ten days there were about 2,000 cases. This included not only those who were sent to the hospitals, but also those who were cared for in barracks. “This was the only division that remained in this country without change of station from April until the fall of 1918.