This report presents the findings of the “BY-COVID Spring 23 Use Cases Workshop Integration of socioeconomic data in observational studies on vaccine effectiveness”. The workshop was organised in the context of the BY-COVID project work package 5 (WP5) “A continuously evolving demonstrator project feeding the changing research questions that surface during an on-going pandemic to solutions” with the support of WP6 “Engage, train and build capacity with national and international stakeholders”. The event took place in The Hague, the Netherlands at the premises of NWO, the Dutch Research Council on April 26th 2023 and was co-organised by CESSDA/KNAW-DANS, Sciensano, and IACS. A particular focus was placed on the Netherlands and Belgium, featuring multiple key actors predominantly from the social sciences domain, both internal and external to the BY-COVID project. Bringing together a diverse group of stakeholders, the workshop aimed to achieve the following goals: To promote further development of the BY-COVID Baseline Use Case, and stimulate community discussion around it; To highlight relevant initiatives and practices in the Dutch and Belgian landscape; To discuss issues surrounding socioeconomic data requirements, mobilisation, and protection in different national contexts in the form of breakout sessions; To highlight how real-world vaccine effectiveness can be estimated in a causal framework by combining administrative, health and care data with data on socioeconomic factors. The workshop report further describes the workshop, highlights the main points of discussion, and identifies outcomes and implications for the project moving forward. The report is a collaborative effort with contributions from workshop participants, and other community stakeholders. It also aspires to be of further use for the BY-COVID project and relevant initiatives.