Phase 3 Infant Safety & Immunogenicity Trial of MVA-BN® in DRC

This Phase 3 double-blinded, randomized study aims to evaluate the safety and immunogenicity of the two-dose MVA-BN mpox vaccine regimen, administered subcutaneously, in infants and children aged 4 to 24 months in the Democratic Republic of the Congo (DRC), a population at high risk of mpox infection and complications. The study will compare the safety and immunogenicity of a full-dose regimen versus a half-dose regimen in this population. A hierarchical testing strategy will be applied as follows: first, non-inferiority of the full-dose regimen in infants/children (4-24 months old) will be evaluated against the full-dose regimen in adults from the POX-MVA-045 study. If non-inferiority is demonstrated, the immunogenicity of the half dose in infants/children (4-24 months old) will subsequently be tested for non-inferiority vs the full dose in adult. The trial will be conducted in Boende, Tshuapa Province, DRC. The trial plans to enroll 344 male and female infants/children, who will be randomized to receive two doses of the MVA-BN vaccine administered 28 days apart. Participants in Child Group 1 (N=172) will receive the standard vaccine dose (0.5 mL), while those in Child Group 2 (N=172) will receive half the standard dose (0.25 mL), with both groups following the same dosing schedule. This study builds on positive safety and immunogenicity data from prior trials that support the use of the standard dose regimen in younger children. However, considering the developmental differences in the immune systems of infants and young children/adolescents, it aims to evaluate whether a half-dose regimen can provide similar immunogenicity while potentially reducing reactogenicity. The findings will offer valuable insights into the optimal dosing strategy for this age group, balancing safety and immunogenicity to inform future vaccination recommendations.