Dengue is an epidemic in Sri Lanka and is one of the fastest spreading mosquito-borne viral diseases in the world. It is considered by the Word Health Organization as one of the top ten global threats to health in 2019. Takeda’s tetravalent dengue vaccine trial, DEN 301, is therefore of high relevance to Sri Lanka. DEN 301 is a study designed to evaluate the efficacy, safety and immunogenicity of two doses of tetravalent dengue vaccine (TAK 003), in both dengue exposed and naïve patients. The study is being conducted in Sri Lanka in collaboration with the Epidemiology Unit of the Ministry of Health. Project management is done by RemediumOne under the guidance of the University of Kelaniya. The trial is currently running in 4 centers situated in dengue prevalent areas in Sri Lanka. 2100 healthy volunteers between the ages of 4 to 16 have been recruited into the study and are being followed up weekly. Maintaining a 99% retention rate as of date, one of the key success factors of the study is the commitment of the investigators and effective management of all stakeholders. This first analysis of the trial showed that the investigational live-attenuated tetravalent dengue vaccine (TAK-003) was efficacious in preventing dengue fever caused by any of the four serotypes of the virus. While review of the extensive data set is ongoing, TAK-003 was well tolerated with no significant safety concerns to date. The trial is continuing and additional results are expected later this year.