Background: Limited studies have been conducted on access to COVID-19 vaccines and identifying the most appropriate health centres for performing vaccination in metropolitan areas. This study aimed to measure potential spatial access to COVID-19 vaccination centres in Mashhad, the second-most populous city in Iran.Methods: The age structure of the urban census tracts was integrated into the enhanced two-step floating catchment area model to improve accuracy. The model was developed based on three different scenarios: only public hospitals, only public healthcare centres, and the top 20% healthcare centres were employed as potential vaccination facilities. The weighted decision-matrix and analytic hierarchy process based on four criteria (i.e. service area, accessibility index, capacity of vaccination centres, and distance to main roads) were used to choose potential vaccination centres with the highest suitability for residents.Results: Our findings indicate that including the both public hospitals and public healthcare centres can provide high accessibility to vaccination in central parts of the urban areas. However, using only public healthcare centres for vaccination can provide higher accessibility to vaccination sites in the eastern and north-eastern parts of the study area. Therefore, a combination of public hospitals and public healthcare centres is recommended for efficient vaccination coverage.Conclusions: Measuring spatial access to COVID-19 vaccination centres can provide valuable insights for urban public health decision-makers. Our model, coupled with geographical information systems (GIS), provides more efficient vaccination coverage by identifying the most suitable healthcare centres, which is of special importance when only few centres are available.