Resolving stark differences between rich and poor countries in vaccine coverage against COVID is a global policy priority for 2022. However, even among OECD countries, there currently remain surprisingly large differences in vaccine coverage and this paper attempts to explain these differences, including the role that policy has played. The main findings are: vaccination has had massive health and economic benefits; vaccine hesitancy can be overcome, although there remains a link with historical flu and MMR vaccination rates; well-designed vaccine passes can boost coverage; trust in government and other public institutions matter, although the link to vaccine coverage is not straight-forward; demographic structure and policy stances towards vaccinating children play a role in explaining differences in overall population vaccination rates; mandatory vaccination has been implemented or is being considered in a few OECD countries, although it is too early to assess the effects. Finally, case studies of the most successful vaccination campaigns provide additional illumination, which cannot easily be captured in multi-country correlations.