Fidelity research can help to answer essential questions about the diffusion process of innovative health interventions and provide insights for further scaling-up and institutionalization. This study assessed fidelity and reinvention in the implementation of a community-based control strategy for Aedes aegypti control. The intervention was implemented in 16 study areas in La Lisa, a municipality of Havana, Cuba. Its major components were: organization & management, capacity-building, community work and surveillance. A participatory assessment of process data was performed to determine whether the components and subcomponents were implemented, not-implemented or modified. Frequencies were tabulated over all circumscriptions (lowest level of local government) and the average was calculated for the four components. Spearman Rank correlation coefficients were calculated to explore the relationships between components. In addition, semi-structured interviews were conducted with co-ordinators of the strategy at different levels to identify difficulties encountered in the strategy's implementation. Surveillance was the most implemented component (72.9%) followed by capacity-building (54.7%). Community work and organization & management were less implemented or modified (50% and 45%, respectively). Apart from surveillance and capacity-building, all components are significantly and strongly correlated (Spearman Rank correlation coefficient > 0.70, P < 0.01). If one component is implemented in a circumscription, the other components are also likely to be implemented. It is noticeable that areas which did not undergo organizational changes commonly did not implement community work activities. Within the whole strategy, few activities were added. Scarcely implemented subcomponents were the most innovative. The difficulties encountered during implementation were related to appropriate training and skills, available time, lack of support and commitment to the strategy, lack of motivation of local leadership, and integration of actors and resources. The study showed a wide variability of fidelity in the implementation of the intervention and highlighted challenges for scaling-up and institutionalization of the community-based intervention.