Dengue is the most prevalent arboviral infection globally, causing significant morbidity and mortality. No specific treatment exists, and the first licensed dengue vaccine, Dengvaxia, is not widely used due to safety concerns. The recent approval of the second-generation vaccine, Qdenga, is thus an exciting development. However, the four immunologically interacting dengue serotypes complicate vaccine development and evaluation. Therefore, Qdenga's phase III trial data must be carefully interpreted, and the vaccine's potential impact across transmission settings needs to be estimated. This thesis uses the currently available data to characterise Qdenga's immunogenicity, efficacy, and impact. I developed a biologically motivated survival model and calibrated it to phase III data to estimate Qdenga's efficacy profile, showing that mean-neutralising antibody titre dynamics can explain vaccine-associated protection at the population level. The results show that Qdenga's efficacy depends on serotype, serological status, and age, with high protection in seropositive individuals and against serotype 2. However, I cannot rule out a disease enhancement risk in seronegative children, particularly those aged 4-5 years. Comparing Qdenga's efficacy profile with Dengvaxia reveals key safety and efficacy differences, supporting further evaluation of Qdenga. I then translated Qdenga efficacy estimates into population-level impact using a four-serotype transmission model, showing that vaccinating children over six years in moderate to high transmission settings could reduce hospitalised cases by up to 10-20% over ten years. The benefits in lower transmission settings are uncertain, highlighting the need for additional post-licensure data. Finally, to further our understanding of serotype-specific and cross-reactive immunity, I analysed serological data and trained machine learning models to predict the infecting serotype, demonstrating their potential in understanding infection histories and evaluating clinical trial endpoints. Overall, this thesis characterises antibody dynamics and Qdenga's efficacy and public health impact, supporting its targeted use in high transmission settings to reduce the growing dengue burden.