Study VLA1553-221 was a randomized, double-blind, phase 2 trial testing a live attenuated chikungunya vaccine in 304 healthy children aged 1 to 11 years in Honduras and the Dominican Republic[1]. The children were divided into groups that received either a full dose or a half dose of the vaccine[1]. The vaccine was well tolerated regardless of dose size or prior chikungunya infection, and no safety issues were identified[1][2]. The full dose elicited a more robust immune response compared to the half dose, with 96.5% of chikungunya-naïve children achieving protective antibody levels 180 days after vaccination[1][2]. The immune response in children was comparable to that seen in adults and adolescents[1][2]. Based on these results, the full dose was selected for future phase 3 clinical trials in the pediatric population[1].