Sex and gender differences in morbidity and mortality from influenza-like illness during pandemics and throughout the 20th century in Switzerland

BACKGROUND: Influenza-like illness (ILI) affects women and men differently. These differences are due to a number of factors, with women often being more exposed and susceptible to ILI infections, while men are at higher risk of mortality. Little is known about how far back these differences reach in history. OBJECTIVES: We investigated sex and gender differences in morbidity, mortality and work absenteeism in Switzerland with never-before-used historical 20th century data. METHODS: We analyzed several historical data series: Swiss-wide ILI/pneumonia mortality 1910-2022; ILI mortality/morbidity 1918-1929 in Basel-Stadt; and ILI-related insured sick days in 1918 from insurance companies. In addition, we analyzed sickness-related work absenteeism in a large company (Swiss Re) in Zurich 1918-1965 and in the national Swiss Postal Service 1902-1993. RESULTS: In all age groups, men had a higher ILI/pneumonia mortality risk than women, although these differences vary across time and age groups. In contrast, both morbidity in Basel-Stadt in the 1920s and the number of insured sick days in six selected insurance companies during the 1918 pandemic were higher for women than for men. Work absenteeism was also higher for women in both analyzed companies during the twentieth century. For the Swiss Postal Service, we find that during ILI epidemics and pandemics, work absenteeism was even higher among women than men. CONCLUSION: We confirm that ILI/pneumonia mortality was higher in men than in women. We also find indications that women were more affected by ILI morbidity, including work absenteeism, which could be due to additional social gender effects.