Composite scores and quantitative correlations are thus useful, but alone are insufficient tools for determining causal relationships between health system capacities and observed health outcomes. The GHS Index’s transparent accounting of country capacities across various domains of health security is intended to function as a gateway to more nuanced case study analyses, in-country evaluations or after-action assessments that could help elucidate the causal mechanisms underpinning observed health outcomes during or after an outbreak. These latter approaches are better-suited to answering why, with respect to COVID-19, high-scoring countries like the USA, the UK, Sweden and Brazil have fared significantly worse than similarly high-ranked states like Thailand, and even compared with lower-ranked states like New Zealand, Vietnam and the Republic of Korea.