Phase 2 Randomized, Open-Label Trial of Intradermal vs. Subcutaneous MVA-BN Vaccine Booster for Mpox Immunogenicity in Previously Vaccinated Individuals

The primary objective of this study is to evaluate whether an **MVA-BN** booster dose administered intradermally (ID) is non-inferior to subcutaneous (SC) administration in inducing a detectable humoral immune response at one month. This is clinically relevant as it may offer an alternative route of administration for the prevention of **monkeypox (mpox)** infection, potentially improving vaccine accessibility and patient compliance.

Secondary objectives include:

• Determining if an MVA-BN booster dose administered ID is non-inferior to SC in inducing a detectable humoral immune response at six months.
• Comparing MPXV-specific immune responses between booster doses administered ID versus the control arm, and SC versus the control arm at one and six months post-booster or post-inclusion.
• Studying the durability of humoral immunogenicity, including the duration of detectable antibodies, peak titres, and subsequent decay, following a booster dose, considering the route of administration and time since primary vaccination.
• In an immunophenotyping sub-study, describing and comparing the magnitude, stability, and phenotypic characteristics of MPXV- and MVA-BN-specific memory plasma and B cell responses, as well as cellular responses by study arm.
• Studying and comparing mucosal (oral and rectal) IgA and IgG antibodies by study arm at various time points up to 24 months.
• Describing serious adverse reactions of a booster dose by route of administration, dose interval, sex, and HIV status.
• Describing and comparing breakthrough infections by study arm, number of doses, route of administration, dose interval, sex, and HIV status up to 24 months.

The clinical trial focuses on the **prevention of monkeypox (mpox) infection** and involves a study population comprising both male and female adults aged 18 years and older. Participants are required to have received a dose of the MVA-BN vaccine at least four months prior to the study. The trial does not include vulnerable populations. The selection criteria emphasize individuals who are willing and able to participate, have signed written consent, and are expected to be available for monitoring throughout the study period. Specific lifestyle considerations include men who have sex with men at Swedish and Irish trial sites, and women at French trial sites must test negative in a pregnancy test. The sponsor has not provided information regarding the total number of participants in the trial.

The clinical trial is designed as a **Phase II randomized, open-label study** to evaluate the immunogenicity and safety of a booster dose of the **Modified Vaccinia Ankara – Bavarian Nordic Live Virus** vaccine for the prevention of **monkeypox (mpox) infection**. The trial will compare the immune response elicited by intradermal (ID) versus subcutaneous (SC) administration of the booster dose. The primary objective is to determine if the ID booster is non-inferior to the SC booster in inducing a detectable humoral immune response one month post-booster. The trial is expected to commence on January 1, 2025, and conclude by March 31, 2028, with participant involvement lasting up to 24 months.

Participants will undergo a series of study visits, beginning with an inclusion (screening) visit to confirm eligibility based on criteria such as age (≥18 years), previous vaccination with the MVA-BN vaccine, and availability for the study duration. Follow-up visits will occur at Day 0 (baseline), Day 7 (for a subset of participants), and at months 1, 3, 6, 12, and 24 post-booster. These visits will assess the primary and secondary endpoints, including the presence of MPXV- and vaccinia virus-binding antibodies, geometric mean titers, and sero-response rates. The end-of-study visit will finalize data collection and assess long-term safety and immunogenicity outcomes.

Participants are expected to remain in the study for the entire duration unless conditions arise that necessitate early termination, such as serious adverse reactions or withdrawal of consent. The trial will monitor the incidence of serious adverse reactions and breakthrough infections throughout the study period. The study aims to provide valuable insights into the optimal administration route for the MVA-BN booster dose, contributing to enhanced protection against mpox.

The clinical trial involves the administration of **Modified Vaccinia Ankara – Bavarian Nordic Live Virus** as the experimental medication. This vaccine is provided in the form of a **suspension for injection**. Two different administration routes are utilized in the study: **subcutaneous injection** and **intradermal use**. For the subcutaneous route, the maximum daily dose is 0.5 ml, with the same amount being the total dose administered over the treatment period. The intradermal route involves a maximum daily dose of 0.1 ml, which also represents the total dose for the treatment period. The treatment period for both administration routes is limited to one day. The vaccine is not formulated specifically for pediatric use, and it is classified as a structurally diverse substance, specifically a vaccine.

In this trial, there are no non-experimental treatments such as standard-of-care therapy, placebo, or comparator treatments being utilized. The primary objective of the trial is to assess the immunogenicity and safety of the booster dose of the MVA-BN vaccine, comparing the intradermal administration to the subcutaneous administration in terms of inducing a detectable humoral immune response one month post-vaccination. Participant compliance with the dosing schedule is monitored to ensure adherence to the protocol, although specific compliance monitoring methods are not detailed in the provided data.

Efficacy in this clinical trial will be assessed by evaluating the humoral immune response following administration of a booster dose of the **MVA-BN** vaccine. The primary endpoint is to determine the non-inferiority of the intradermal (ID) booster dose compared to the subcutaneous (SC) booster dose in inducing detectable **MPXV**- and vaccinia virus-binding antibodies (BAbs) at one month post-booster. This will be measured by ensuring that at least 80% of participants in both booster arms have detectable BAbs, with a maximum allowable difference of 10% between the two groups.

Secondary endpoints include assessing the non-inferiority of the ID and SC booster arms in maintaining detectable BAbs at six months post-booster, with the same criteria as the primary endpoint. Additionally, the trial will compare the **MPXV** and vaccinia virus-specific humoral response between the ID booster arm versus control, and the SC booster arm versus control at one and six months post-inclusion. This will involve measuring geometric mean titers (GMTs) of **MPXV**- and vaccinia-specific microneutralizing antibodies (NAbs) and BAbs, as well as changes in sero-response rates (SRRs) in detectable antibodies.

The humoral response will be further evaluated by route of administration over time, with assessments at various timepoints including Day 0, Day 7, Month 1, Month 3, Month 6, Month 12, and Month 24. This will include GMTs of **MPXV**- and vaccinia virus-binding antibodies and microneutralization antibodies, and SRRs from Day 0 forward up to Month 24. In a subgroup of participants, the trial will assess the number, diversity, and functionality of **MPXV**- and **MVA-BN**-specific memory plasma cells and B cells, as well as T-cell responses using ELISpot assays. Additionally, mucosal IgA and IgG antibody responses will be evaluated using ELISA MSD at specified timepoints.

Safety and efficacy will also be monitored through the incidence and relationship of serious adverse reactions (SARs) throughout the study duration, and the cumulative incidence and clinical presentation of breakthrough infections, defined as serologically or PCR-confirmed **MPXV** infections by study arm.