The Spanish Flu was a severe influenza pandemic at the end of the First World War. Contrary to what was long assumed, however, this flu did not affect vulnerable and healthy young people equally hard. This emerges from a current study for which skeletal remains from this period were analyzed. Research had previously assumed, based on anecdotal evidence, that young, healthy people were just as likely to die from influenza as young people with previous illnesses. The refutation of this thesis fits with observations of today's pandemics.
During the flu pandemic that raged between 1918 and 1920, also known as the Spanish flu, it is estimated that up to 50 million people died worldwide. It was the most severe pandemic to date caused by an influenza virus, with a death rate of between five and ten percent of all those infected. Because many people at that time - including young, apparently healthy people - became ill and died within a short period of time, doctors assumed that healthy people were just as susceptible to the disease as the frail. Numerous historical reports, including population statistics and life insurance records, support the theory that the Spanish Flu disproportionately affected young, healthy people between the ages of 15 and 34.
Who was most affected by the Spanish flu?
The two anthropologists Amanda Wissler and Sharon DeWitte have now investigated for the first time whether this is actually true. To do this, they analyzed skeletal remains of 369 people who died in Cleveland, Ohio between 1910 and 1938, i.e. before and during the influenza pandemic. Unlike most historical accounts, bones provide clues about people's pre-existing conditions. In their analyses, the researchers identified 248 bone remains from this period that had lesions in young bone tissue as a result of disease or inflammation. How well these bone lesions had healed at the time of death served as an indicator of whether the people were weakened and therefore more susceptible to disease. The scientists explain that unhealed lesions are signs of unhealthy diet and living conditions.
The analyzes showed that the weakest people in health, i.e. those with only unhealed bone lesions, had the highest mortality rates - regardless of whether the people died before or during the pandemic. The risk of death was 2.7 times higher than for people with both healing and unhealed lesions and correspondingly more robust health. These had the lowest mortality rates in the study.
Findings contradict common assumptions
The results contradict the common assumption that the 1918 flu pandemic affected young, healthy people exceptionally hard - possibly because the influenza virus, unlike most pathogens, made no distinction between population groups. Instead, the new data suggests that during the Spanish flu, healthy people were less likely to die than weakened, less healthy people. This contradicts previous assumptions, but is consistent with observations from recent pandemics, the researchers conclude.
“Our social, cultural and immunological living conditions are intertwined and have already shaped the lives and deaths of people in the distant past,” explains Wissler. “Most recently, we saw during Covid-19 that our backgrounds influenced who was more likely to die and who survived,” she says. The observed “selective mortality”, in which the most frail are most likely to die, is a typical principle of diseases, even with previously unknown pathogens in pandemics. According to current research, risk factors for mortality from infectious diseases such as influenza also include previous illnesses such as asthma or cardiovascular disorders.
Overall, the new study illustrates how anthropological research can improve understanding of past and present pandemics. The researchers want to further investigate the connection between socioeconomic status and mortality in future work. In particular, they want to examine whether their findings from Cleveland apply to other cities in the United States that had different demographics during the Spanish flu or took different measures to combat the pandemic.
Source: Amanda Wissler (McMaster University) et al., Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2304545120