The Covid-19 pandemic has raised concerns about the resilience of health systems. The aim of this study is twofold: i) to measure and compare the resilience of health system efficiency of OECD countries before and during Covid-19 and ii) to determine the healthcare efficiency drivers (e.g., socioeconomic) of health system performance. Using a dataset of 31 OECD countries for 2018 and 2020, we first estimate bias-adjusted efficiency scores, followed by a double bootstrap truncated regression procedure to study the drivers associated with health system efficiency. We find that the health system efficiency overall score decreased among OECD countries during the Covid-19 pandemic compared to before Covid-19. Estonia and Japan retained their full efficiency scoreduring Covid-19. We find a negative association between health system efficiency and unemployment rate, share of health expenditure in GDP, and share of population over 65. Conversely, high vaccination rates contribute positively to health system efficiency during the Covid-19 period.