Scientists from Okayama University Analyze Global Trends in Influenza-Associated Mortality

Japanese researchers analyze the impact of geographical differences and income on seasonal influenza-related deaths between 2001 and 2018

OKAYAMA, Japan, Sept. 1, 2023 /PRNewswire/ — Influenza, a major respiratory infection, is responsible for many deaths across the globe, annually. Researchers from Japan have now used WHO mortality data to analyze trends in influenza-associated mortality. Their findings revealed that death rates are consistently rising since 2009 with variations influenced by geography and income levels. This study data serves as a benchmark for public health providers and policymakers to combat influenza-associated mortality.

Influenza is a leading cause of respiratory diseases, contributing to a significant number of deaths worldwide. To understand the current impact of influenza on global health, a research team led by Professor Hideharu Hagiya and Professor Toshihiro Koyama of Okayama University, Japan, analyzed the trends in seasonal influenza-associated mortality using data from the World Health Organization (WHO) mortality database. Their findings were made available online on June 16, 2023, in the Journal of Infection.

First, the team acquired detailed death count data caused by seasonal influenza in 65 countries, between 2001 and 2018. “We assessed influenza-associated mortality using two parameters: crude mortality rate (CR) and age-standardized mortality rates, considering age structure variations among populations. The analysis, utilizing locally estimated scatterplot smoothing curve, offered insights into global and long-term patterns,” explains Prof. Koyama.

The study revealed a concerning 4.8-fold increase in influenza-associated mortality from 2009 to 2018. Geographically, all five regions, selected based on WHO country groupings, exhibited a rising trend in mortality rates, with Western Europe, North America, and the Western Pacific experiencing faster increases. Age-wise, influenza CR increased in all regions, but a decline was observed among the older population in Eastern Europe and Central and South America.

Income-level analyses revealed that the high-income group demonstrated an upward trajectory from 2009 onwards, while the upper-middle income group maintained a stable rate with recent increases. In contrast, the lower-middle and low-income groups showed steady or decreasing mortality rates.

Despite a decline in mortality rates from 2001 to 2009, the global trend reversed and continued to increase after 2009. This can be attributed to factors such as genetic drift, herd immunity, early treatment due to rapid diagnostic tests, and the development of neuraminidase inhibitors. Discussing the future implications, Prof. Koyama muses, “Our findings can increase the international attention to influenza, encouraging more countries to focus on influenza surveillance and prevention, eventually enhancing global health. We also hope that researchers who wish to use international health databases to improve global health find this study useful.”


Title of original paper: Global trends of seasonal influenza-associated mortality in 2001–2018: A longitudinal epidemiological study

Journal: Journal of Infection


Media Contact:

Toshihiro Koyama

SOURCE Okayama University