Look back at the chronicle of global pandemics, and the flu pandemic of 1918 stands out as an anomaly for one reason: According to the history books, it struck healthy adults in their prime just as often, if not more so, than the weak or sickly.

This assumption has influenced research and literature for decades.

But new research published Oct. 9 in the journal PNAS suggests it may not be true at all.

In examining the skeletal remains of nearly 400 individuals, researchers from the University of Colorado Boulder and McMaster University found that in 1918—just like in 2020—people exposed to environmental, social or nutritional stressors before-hand were significantly more likely to succumb to a novel virus when it emerged.