Measuring health system resilience: Understanding the relationship between excess mortality and health system performance

The COVID-19 pandemic has underscored the importance of resilient health systems that can manage and adapt to large-scale health crises. However, the relationship between resilience and health system performance remains unclear. While some view performance as a feature of resilience, others conflate the two. Excess mortality-defined as the difference between observed and expected deaths during a given period-is often used to assess resilience, but may introduce bias. In particular, countries with stronger pre-pandemic performance and lower baseline mortality may appear to have worse resilience simply because they had less "room" for mortality to rise under normal conditions. This study examines the relationship between pre-pandemic health system performance and resilience, as measured by excess mortality during the first two years of COVID-19. Using the Healthcare Access and Quality (HAQ) Index, we evaluate baseline performance across 194 countries and compare it to age-standardized excess mortality from three major sources. Our analysis shows that health systems with higher pre-pandemic HAQ scores generally experienced lower excess mortality, though the strength of this association varied by data source and was most consistent in the second year of the pandemic. Adjusting for baseline performance using a normalized threshold of pre-pandemic performance, rather than country-specific baselines, improved comparability of excess mortality across countries. These findings suggest that higher baseline performance may enhance resilience to health crises, and that normalizing baselines could yield more accurate cross-country resilience assessments.