Uncovering the toll of the first three COVID-19 waves: excess mortality and social patterns in Belgium.

Background: This study aims to assess which population groups experienced the heaviest mortality burden during the first three COVID-19 waves in Belgium; and investigate potential changes in social differences in all-cause mortality during the epidemic and compared to the pre-COVID period.

Methods: Exhaustive all-cause mortality information (2015-2021) from the Belgian population register was linked to demographic and socioeconomic census and register data. Annual cohorts consisting of 6.5 million to 6.8 million persons were created selecting persons aged 35 and older. Excess mortality was investigated comparing the 137,354 deaths observed during the first three COVID-19 waves with mortality in the reference period 2015-2019. Methods of analysis include direct standardization and Poisson regression analyses.

Results: Elderly men experienced the highest absolute mortality burden during all three COVID-waves, followed by elderly women, middle-aged men, and middle-aged women. Care home residents consistently experienced higher mortality rates during the first and second wave compared to peers living in other living arrangements. In wave 3, care home residents showed significant absolute mortality deficits compared to the reference period. When adjusting for all demographic and socioeconomic factors, the traditional pattern of educational and income mortality inequalities was found among the elderly population during the COVID-waves. In contrast, the educational mortality gap among middle-aged persons deepened during COVID-waves 2 and 3 with excess mortality between 19 and 30% observed among mainly lower-educated persons. Income mortality inequalities among middle-aged women and men remained stable or even diminished for some specific groups in some waves.

Conclusion: The widening educational mortality gap among middle-aged persons in successive waves suggest an important role of knowledge and associated educational resources during the COVID-19 epidemic. Belgium's broad implementation of public health control and prevention measures may have successfully averted a further widening of social mortality inequality between income groups and among the elderly population.