Study of 1918 flu contradicts belief that healthy young adults were more vulnerable

TORONTO: An international team of researchers studying the remains of 1918 flu pandemic victims found that frail and young adults were more likely to die, contradicting the widespread belief that the flu disproportionately impacted healthy young adults.

The 1918 influenza pandemic, commonly referred to as the “Spanish flu”, killed an estimated 50 million people worldwide -- claiming more lives than World War I.

Because so many people fell ill so quickly, physicians at the time believed the healthy were as likely to die from the flu as those who had already been sick or frail.

Despite numerous historical accounts, though, it turns out there is no concrete scientific evidence to support that belief.

Researchers at McMaster University in Canada and the University of Colorado Boulder who analysed victims' age of death and studied lesions on victims' bones report that the most susceptible to dying of the flu had exhibited signs of previous environmental, social, and nutritional stress.

"Our circumstances -- social, cultural and immunological -- are all intertwined and have always shaped the life and death of people, even in the distant past," said lead author Amanda Wissler, Assistant Professor in the Department of Anthropology at the University of McMaster.

"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," she said.

Much of the research on the 1918 pandemic relies on historical documentation such as vital statistics, census data and life insurance records, none of which include information on pre-existing conditions, or general environmental, dietary or other chronic stressors which can impact one's overall health over the course of a lifetime.

For the study, published in the journal PNAS, researchers examined the skeletal remains of 369 individuals from the Hamman-Todd Documented skeletal collection, which is housed at the Cleveland Museum of Natural History.

All had died between 1910 and 1938.

The sample was divided into two groups: a control group who had died before the pandemic, and those who died during the pandemic.

A living person's skeletal structure may undergo lasting changes due to poor health, resulting in diminished height, irregular growth, developmental tooth defects and other indicators.

The team searched for lesions, or indicators of stress, on the shin bones of the pandemic victims. New bone formation occurs in response to inflammation caused by physical trauma or infection, for example.

Researchers can determine if a lesion had been active, in the midst of healing or had completely healed, all of which provide evidence of underlying conditions.

"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," said co-author Sharon DeWitte, a biological anthropologist at the University Colorado-Boulder.

Pre-existing medical conditions such as asthma or congestive heart failure are common risk factors which can contribute to poor outcomes from infectious diseases such as influenza. Racism and institutional discrimination can amplify these effects, as evidenced in the Covid-19 pandemic, said the researchers.