This is a multi-center, double-blinded, placebo-controlled, Phase II study to evaluate safety, tolerability, and immunogenicity of a single dose of cAd3-Marburg vaccine in healthy adults up to 70 years of age, in Uganda and Kenya. The study will enroll 125 eligible participants randomized 4:1 to receive the cAd3-Marburg vaccine at 1.0 × 10^11 PU dose or placebo (0.9% sodium chloride (NaCl) solution) at Day 1, intramuscularly in deltoid muscle. Participants will be screened for eligibility up to 28 days before enrollment. Enrollment will be staggered, starting with healthy adults 18 to 50 years of age (inclusive). Upon enrollment of minimum 25 younger adult participants (sentinel), the safety data up to 7 days post vaccination of these 25 sentinel participants will be reviewed by the independent DSMB. Progression to enrollment of the older adults (>50 to 70 years of age) will be dependent on the unblinded review of the Data Safety Monitoring Board (DSMB). Safety and immunogenicity will be assessed at Days 1, 8, 15, 29, 85, 169, and will conclude at the end of study visit on Day 366.

This Phase 2, randomized, double-blind, placebo-controlled study evaluated the safety, tolerability, and immune response of cAd3-Marburg Vaccine in healthy adults up to 70 years of age at 2 sites in Africa (Uganda and Kenya). Overall, a total of 101 participants received the cAd3-Marburg Vaccine and 25 participants received the placebo. A majority of the participants completed the study with study discontinuation in 3 participants in the cAd3Marburg Vaccine group and 1 participant in the placebo

group. All randomized participants were included in the FAS and Safety Set. The PPS included 99 participants in the cAd3- Marburg Vaccine group and 24 participants in the placebo group. 

The demographic and baseline characteristics were balanced between the cAd3-Marburg Vaccine and placebo groups. The medical history was characteristic of the study population of healthy adults. 

Background Information: 

Marburg virus (MARV) is one of the 6 genera in the family Filoviridae, which, along with Ebolavirus and Cuevavirus, are known to induce viral hemorrhagic fever. MARV is a large, negative-strand RNA virus composed of 7 genes encoding viral proteins, including a single GP. In humans, MARV is responsible for causing MVD, formerly known as Marburg hemorrhagic fever. It spreads through human-to-human transmission, with infection resulting from direct contact with blood, secretions, organs, or other bodily fluids of infected people and indirect contact with contaminated environments. MVD has an incubation period of 2 to 21 days followed by a rapid and abrupt onset of non-specific symptoms such as fever, extreme fatigue, gastrointestinal complaints, abdominal pain, anorexia, headache, myalgias,

and/or arthralgias, and diarrhea can persist for a week. Many patients develop severe hemorrhagic manifestations, including hemorrhagic rash, epistaxis, mucosal bleeding, hematuria, hemoptysis, hematemesis, melena, conjunctival hemorrhage, tachypnea, confusion, somnolence, and hearing loss between 5 and 7 days after infection. Laboratory findings include low white blood cell and platelet counts and elevated liver enzymes (WHO 2021). In the last decades, MARV has been associated with large outbreaks of MVD in Africa; the average case fatality rate is around 50%, varying from 23% to 90% depending

on virus strain and case management (CDC 2021).  The MARV is the etiologic agent of MVD and has been associated with 12 major outbreaks; the 2 largest occurring in Africa (Democratic Republic of Congo from 1998 to 2000 and Angola in 2005) that resulted in case fatality rates over 80%. The first recorded case of MVD in Guinea and West Africa occurred in August 2021 and resulted in 1 fatality. Recently 2 fatal cases of MVD were reported from Ashanti region, Ghana in June 2022 (WHO 2022). There is a continued potential threat of spread to other countries given the frequency of international travel (IB 2022). Sabin cAd3-Marburg vaccine is supplied as a single-dose vial that contains a recombinantcAd3 vector that expresses WT GP from the Angola strain of the MARV. The primary goal of

the cAd3-Marburg vaccine is to induce rapid immunity followed by durable protection against MVD.