This paper introduces a methodology to explore pedestrian accessibility in informal settlements. This methodology is applied to pandemic intervention sites in Nairobi's Kibera area for 3.5 months (14 April to 31 July 2020) during the COVID-19 pandemic. Freely available transportation network data and open-source GIS software are utilised. Isochrones, areas of equal travel time, are calculated to assess pedestrian accessibility (walk times) from 30,231 Kibera structures to 138 COVID-19 stationary intervention sites. These sites aid in virus control, resource distribution, and COVID-related medical support. Travel times are determined considering different terrain slopes. Unequal access to intervention sites is observed due to indirect routes. Shortest walks (up to 21.5 min) are to handwashing and food distribution points, while longer walks (up to 61.5 min) are to interventions with fewer sites or localised clustering, such as baby product distribution. This simple accessibility analysis helps identify service gaps during crises, aiding planning authorities and communities. Our methodology offers insight into travel patterns in slums and has wider applicability to assess the relationships between transport infrastructure provision and resilience in informal settlements.