The 1918 Flu Pandemic Did Not Disproportionately Kill Healthy Young People

Researchers from McMaster University and the University of Colorado Boulder analyzed ancient skeletal remains to further understand the death toll of the 1918 influenza pandemic, commonly referred to as the “Spanish flu”.

The pandemic killed ~50 million individuals across the globe, claiming more lives than World War I. For many years, scientists have been puzzled by the seemingly high mortality rate among young adults. Because populations fell ill so quickly with the disease, medical professionals at the time assumed that it did not discriminate between the young and healthy, or the sick and frail. “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,” the research team behind the study writes in PNAS.

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The 1918 Flu Pandemic

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Much of the research conducted on the pandemic has utilized historical documents, including census data, life insurance records and vital statistics. Such records fail to document information on any pre-existing medical records, a patient’s environment, diet or lifestyle stressors.

Dr. Amanda Wissler, an assistant professor in the Department of Anthropology at McMaster, led the research team in their analysis of 369 skeletal remains obtained from the Hamman-Todd Osteological Collection, housed at the Cleveland Museum of Natural History. The remains were from individuals that had died between 1910 and 1938. Wissler and team divided the remains into two categories for their analyses: those who died during the pandemic and a control group who died before the pandemic.

Frail or unhealthy individuals were more likely to die during the pandemic

Wissler and colleagues scoured the shinbones of the skeletal remains for lesions, areas of bone that are changed or damaged. Fractures, tumors and inflammation triggered by infection can cause lesions.

The research team was able to conclude whether a lesion had been active, healing or had completely healed at the time of the individual’s death, which helps create a clearer picture of whether that individual was suffering from underlying conditions.

“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 research team describes.

“By comparing who had lesions, and whether these lesions were active or healing at the time of death, we get a picture of what we call frailty, or who is more likely to die. Our study shows that people with these active lesions are the most frail,” Professor Sharon DeWitte, a biological anthropologist at the University of Colorado Boulder and co-author on the study, says.

“Our circumstances – social, cultural and immunological – are all intertwined and have always shaped the life and death of people, even in the distant past,” explains Wissler. “We saw this during COVID-19, where our social backgrounds and our cultural backgrounds influenced who was more likely to die, and who was likely to survive.”

“The results of our work counter the narrative and the anecdotal accounts of the time,” adds Wissler. “This paints a very complicated picture of life and death during the 1918 pandemic.”

Going forward, the team intends to continue their exploration of mortality and socioeconomic status.

Reference: Wissler A, DeWitte SN. Frailty and survival in the 1918 influenza pandemic. PNAS. 2023;120(42):e2304545120. doi: 10.1073/pnas.2304545120

This article is a rework of a press release issued by McMaster University. Material has been edited for length and content.