The two primary narratives that have emerged to explain low COVID-19 vaccine uptake in low- and middle-income countries are constrained accessibility and vaccine hesitancy. However, it is unclear how much each issue contributes to low uptake. This article examines these twin barriers to access. Using global survey data from 15,696 respondents across seventeen Western Pacific and African countries, collected between May 2022 and January 2023, we estimated the unmet demand for vaccines and examined its predictors. We found that among unvaccinated respondents, by the time of the survey, 50 percent had unmet demand-meaning they were still willing to get vaccinated. Rates of unmet demand were highest in African countries and lowest in Western Pacific countries. The perceived accessibility of vaccines and respondents' age and sex were identified as consistent predictors of unmet demand. These issues suggest that inequitable supply continues to play a substantial role in limiting vaccine access. Targeted efforts to increase vaccination rates are necessary, particularly in countries with low coverage and high unmet demand. Policy efforts should address barriers to vaccine access, ensure accessibility and distribution of mRNA vaccines, and aim to overcome vaccine hesitancy-all critical factors in reducing unmet immunization demand and achieving higher vaccination rates across regions.