All young adults were at highest risk of dying of influenza, but of these, two groups had especially high mortality rates: males and immigrants. The male mortality rate was fifty percent higher than the female rate, and the chances of death increased in foreign-born individuals. Some researchers have suggested that this is due to social and cultural behaviors. Young men were less likely to stay at home and rest when ill, allowing the disease to progress beyond the point of treatment. Usually, they also spent more time out of the home than women did, and daily contact with new microbes gave them stronger immune systems than females, increasing their chances of developing fatal cases of influenza or pneumonia. Immigrants were unfamiliar with American public health and healthcare systems and practices and did not seek care due to differing ethnic beliefs and language barriers.
These cultural factors certainly played a role in male and immigrant susceptibility, but the biggest risk factors, especially for immigrants, were biological. Researchers surmise that previous influenza epidemics granted many individuals some immunity to the 1918-1919 virus. However, these epidemics primarily affected urban areas. The immigrant rush of the early twentieth century brought thousands of men and women between the ages of 20 and 40 to the United States, most from rural areas of Eastern and Southern Europe. Their lack of exposure to disease, especially compared to their American neighbors in crowded workplaces and urban tenements, made them especially susceptible to influenza in 1918.
Influenza killed with no regard for physical strength, gender, race, or ethnicity, and indigenous peoples around the world, however isolated, suffered exceptionally high morbidity and mortality rates during the pandemic. The relative isolation of many indigenous peoples meant they had little or no natural immunity to pathogens of any kind and little or no access to public health and healthcare resources. The lethal virus of 1918-1919 killed entire villages in the remote corners of Alaska and decimated populations in the Pacific islands. In the United States, the Native American mortality rate was four times that of urban whites. Influenza infected twenty-four percent of those on reservations and the virus killed two percent of the entire Native population between October 1918 and March 1919. The experience of Native populations is an extremely important part of the pandemic narrative, especially for Montana, a state with seven reservations. High mortality rates on reservations may mean that Montana’s overall mortality rate is much higher than originally believed. However, much more study is necessary to understand the impact of influenza on Montana’s reservations and tribal populations.
 Thomas A. Garret, “War and Pestilence as Labor Market Shocks: U.S. Manufacturing Wage Growth, 1914-1919.” Economic Inquiry 47 no. 4 (October 2009), 713; Howard Phillips and David Killingray, introduction to The Spanish Influenza Pandemic of 1918-1919: New Perspectives (London: Routledge, 2003), 8; Crosby, America’s Forgotten Pandemic, 67.
 Walters, “The Contemporary Perspective,” 857; Katz, “A Study in Mortality,” 422; Katz, “Further Study in Mortality,” 619.
 Crosy, America’s Forgotten Pandemic, 231-2; Steele, “Montana Frontier,” 83.