The success of countries in the Organization for Economic Cooperation and Development (OECD) in controlling the COVID-19 pandemic has varied greatly. Explanations for the differences fall into four broad categories: political/economic, cultural/social, demographic/geographic, and policy-oriented. This paper uses Bayesian model averaging to assess the explanatory power of 21 potential covariates. It shows that standard political economy variables that predict greater investment in public health, such as GDP per capita and level of democracy; both general and pandemic-specific measures of government effectiveness; and demographic factors that predict increased vulnerability, such as the share of population that is elderly or obese, do not explain the differences in outcomes. The key factors appear to have been interdictability (the ability to tightly control borders and effectively restrict or monitor entrants at a limited number of entry ports), the early adoption of stronger international travel restrictions, and a female head of government.