Immunogenicity of fractional subcutaneous booster vaccination against mpox: a non-inferiority study

Although mpox incidence has significantly declined since the outbreak in 2022, recurrence of monkey pox virus (MPXV) circulation remains possible. With a continuous risk of reintroduction of MPXV into a highly susceptible population with absent or waning immunity, there is no room for complacency. The relative contribution of vaccination to the interruption of the outbreak is not fully understood. Initial studies showed that the MVA-BN vaccine had low immunogenicity, but that antibody levels are significantly boosted if a third shot is administered one year after the primary vaccination regimen. Aim The aim of this study is to prove that a boost can also be given with a 1/5 fractional dose, and that this is not inferior to the standard dose with regards to the induction of immunogenicity. (Expected) results If fractional dosing proves non-inferior to the standard dose, significant dose-sparing can be achieved with less side effects, which could prove essential in the interruption of future mpox outbreaks.