Widespread uptake of COVID-19 vaccines is necessary to achieve herd immunity . However, surveys have found concerning numbers of U.S. adults hesitant or unwilling to be vaccinated . Online misinformation may play an important role in vaccine hesitancy, but we lack a clear picture of the extent to which it will impact vaccination uptake . Here, we study how vaccination rates and vaccine hesitancy are associated with levels of online misinformation about vaccines shared by 1.6 million Twitter users geolocated at the U.S. state and county levels . We find a negative relationship between recent levels of misinformation and daily vaccination rates . Consistently, negative opinions toward vaccines are correlated with misinformation . Vaccine hesitancy is also strongly associated with Republican vote share, but the association between vaccine outcomes and misinformation remains significant when accounting for political as well as demographic and socioeconomic factors . Hesitancy levels in Democratic counties with high misinformation match those in Republican counties . These results suggest that addressing online misinformation must be a key component of interventions aimed to maximize the effectiveness of vaccination campaigns.