A1168
Title: Disentangling causal effects of reporting delays and immune pressure on COVID-19 mortality and hospitalization rates
Authors: Hsiang-Yu Yuan - City University of Hong Kong (Hong Kong) [presenting]
Abstract: Disentangling direct and indirect effects is key to understanding the outcomes of COVID-19 control efforts. Inequities in socio-demographics and vaccine coverage can drive disease burden, often through mediators such as test-and-trace and SARS-CoV-2 variant dynamics. Causal mediation analysis is applied in two epidemiological contexts (i) variations in case fatality rate (CFR) via reporting delays in Hong Kong and (ii) variations in case hospitalization rate (CHR) via vaccine-induced variant dynamics in the United States to uncover the underlying mechanisms shaping public health outcomes. In Hong Kong, low-income districts exhibited a twofold higher CFR. However, mediation effects of severe reporting delays were weakly present for age and absent for income level, suggesting that mortality disparities were primarily driven by health inequities. In the United States, increased vaccination indirectly reduced the CHR by selecting for less virulent Omicron subvariants since Delta. The resulting dominance of Omicron contributed to a further decline in CHR, complementing the direct protective effect of vaccination. These findings highlight distinct causal pathways shaping COVID-19 outcomes. Public health strategies should, therefore, address both mediating mechanisms (i.e., health system overload and immune-escape variant emergence) and deeper causes, such as socioeconomic inequities, to reduce disease burden.
