A controlled human dengue challenge trial reported how preexisting immunity reshapes secondary infection dynamics and broadly protective immune responses. Across 45 volunteers with different prior dengue infection histories, researchers challenged participants with a live, weakened DENV3 strain and monitored viral replication and immune kinetics. The team reported that antibody profiles linked to boosted viral replication also correlated with weaker T-cell and antibody contraction, while higher antibodies against nonstructural protein 1 associated with more balanced immune responses and lower viral loads. The findings provide mechanistic input for therapeutic and vaccine design by showing how different preexisting antibody landscapes can tilt secondary dengue severity pathways.