Frailty and survival in the 1918 influenza pandemic

Abstract

One of the most well-known yet least understood aspects of the 1918 influenza pandemic is the disproportionately high mortality among young adults. Contemporary accounts further describe the victims as healthy young adults, which is contrary to the understanding of selective mortality, which posits that individuals with the highest frailty within a group are at the greatest risk of death. We use a bioarchaeological approach, combining individual-level information on health and stress gleaned from the skeletal remains of individuals who died in 1918 to determine whether healthy individuals were dying during the 1918 pandemic or whether underlying frailty contributed to an increased risk of mortality. Skeletal data on tibial periosteal new bone formation were obtained from 369 individuals from the Hamann–Todd documented osteological collection in Cleveland, Ohio. Skeletal data were analyzed alongside known age at death using Kaplan–Meier survival and Cox proportional hazards analysis. The results suggest that frail or unhealthy individuals were more likely to die during the pandemic than those who were not frail. During the flu, the estimated hazards for individuals with periosteal lesions that were active at the time of death were over two times higher compared to the control group. The results contradict prior assumptions about selective mortality during the 1918 influenza pandemic. Even among young adults, not everyone was equally likely to die—those with evidence of systemic stress suffered greater mortality. These findings provide time depth to our understanding of how variation in life experiences can impact morbidity and mortality even during a pandemic caused by a novel pathogen.