Infectious diseases and other factors impacting trends in excess mortality for 2010-24 in Poland

Abstract Background During the COVID-19 pandemic, mortality patterns in Poland shifted dramatically. Throughout the study period, all-cause mortality exhibited an upward trend and a strong seasonality. The aim of this study is to estimate the extent of excess mortality attributable to several factors outside of COVID-19: influenza-like illness epidemics, extreme weather events and air pollution. Methods All-cause mortality data were sourced directly from death certificates and integrated with the notifications from the National Health Fund administrative registry as well as the publicly available historical weather database. We estimated baseline weekly mortality using a quasi-Poisson regression model fit to pre-pandemic data (2010-19). We defined excess mortality as the empirical number of deaths surpassing the baseline and attributed specific factors based on their temporal alignment. Results In the pre-pandemic period yearly excess mortality in Poland ranged from 0.8 to 2.9%, whereas in years 2020-22 it soared to 14.8%, 19.7% and 6.4%, respectively, only to stabilise at 1.8% in 2023. Aside from the acute pandemic phase, the share of excess mortality attributable to environmental exposures displayed on average lower burden (14-58% for heat waves, 2.6-20.8% for air pollution and 1.8-13.4% for cold spells) than influenza-like illness epidemics (18.9-74.3%). In years 2020-23 COVID-19 was a major contributor responsible for 96.3%, 96%, 74% and 15.2% of total excess mortality, respectively. Non-COVID-19-attributable excess mortality hit a record low of a meagre 0.5% of all-cause mortality in 2020. Conclusions Excess mortality trends in Poland were interrupted by the COVID-19 pandemic but have since bounced back. Outside of crises, influenza-like illness epidemics remain by far the most contributing factor. Surveillance of excess mortality and the impact of the underlying factors allows for the assessment of general health system performance. Key messages • Outside of crises, influenza-like illness epidemics remain by far the most contributing factor. • Surveillance of excess mortality and the impact of the underlying factors allows for the assessment of general health system performance.