Pandemics, Severity, and Context—Some Loose Ends

Simonsen, Lone; Viboud, Cecile

Quantitative studies of historical pandemic events are key. Because of the dearth of human population experiences with GCBR-type events in the past hundred years, it is critical to conduct careful studies of historical pandemics, starting with the bubonic plague era, in order to elucidate the transmission patterns and impact of past pandemic events in various settings, populations, and circumstances. In European countries, for example, excellent health recordkeeping, availability of population censuses, and other demographic studies allow reconstruction of epidemics of plague, smallpox, cholera, and influenza pandemics over centuries. Also, as regards reemerging threats like yellow fever in Brazil in 2016-17, a careful review of the devastating outbreaks in the Americas in the 19th century would provide a sobering context. A severe pandemic event may not be risky to everyone. As an example, the 1918 pandemic was devastating especially to young adults (about 6% of this age group died), while the elderly were completely spared in many settings, most likely due to immune protection from childhood experience with a similar influenza virus. Thus, profound age-related risk heterogeneity is a scenario that should be taken into account in future pandemics. In addition, heterogeneity could be related to geography, climate, underlying health, and environmental factors, as well as social (exposure limited to a subgroup of the population), behavioral (HIV), and genetic aspects.