Safety, immunogenicity, and optimal dosing of a modified vaccinia Ankara-based vaccine against MERS-CoV in healthy adults: a phase 1b, double-blind, randomised placebo- controlled clinical trial

Background MERS-CoV is a respiratory pathogen with a case-fatality rate of 36%, and for which no vaccines currently licensed. MVA-MERS-S is a candidate vaccine based on recombinant modified vaccinia virus Ankara (MVA). In this study, the safety, immunogenicity, and optimal dose schedule of MVA-MERS-S was assessed in individuals with previous exposure to SARS-CoV-2 infections and vaccines. Methods We conducted a multicentre, double-blind, randomised controlled phase 1b clinical trial at two university medical centres in Germany and the Netherlands. Healthy volunteers aged 18-55 years were assigned by computer randomisation to receive three intramuscular injections of 107 or 10$ plaque-forming units (PFU) of MVA-MERS-S, with two treatment groups each of either 28-day or 56-day intervals between the initial two doses, and one control arm that received only placebo, at a ratio of 2:2:2:2:1. The third dose was given after 224 days. The sponsor, clinical laboratory staff, and participants were masked to both vaccine dose and dosing interval. The primary outcome safety, assessed in the all participants who had received at least one injection; daily solicited vaccine reactions were recorded after each dose for 7 days, unsolicited adverse events for 28 days, and serious adverse events throughout study. The secondary outcome was humoral immunogenicity, measured with vaccine-induced geometric mean antibody concentrations and seroconversion rates, analysed in all participants who received at least three allocated treatments. This study is registered at ClinicalTrials.gov (NCT04119440) and is completed. Findings Between 26 July, 2021, and 3 March, 2022, 244 volunteers were screened, 177 of whom were eligible 140 were randomly assigned either to the 28-day 107 PFU group (n=32), 56-day 107 PFU group (n=31), 28-day 10$ PFU group (n=31), 56-day 10$ PFU group (n=30), or placebo group (n=16). In total, 178 doses were administered of 107 PFU of MVA-MERS-S, 174 of 10$ PFU, and 164 doses of placebo, and 139 participants received least one injection. 73 (53%) were female and 66 (48%) were male. No serious vaccine-related adverse events occurred. Solicited local reactions were mild in 288 (93%, 95% CI 90-96) of 309 reports and consisted primarily of pain tenderness. Pain or tenderness (of any severity) occurred after 69 (39%, 32-46) of 178 107 PFU injections, 138 (79%; 73-85) of 174 10$ PFU injections, and 18 (11%; 7-11) of 164 placebo injections. Of 595 reported solicited systemic reactions, 479 (81%, 77-83) were graded as mild. Systemic reactions of any grade occurred after 77 (43%; 36-51) 107 PFU injections, 102 (59%; 51-66) 10$ PFU injections, and 67 (41%; 34-49) of 164 placebo injections. At 28 days after the second dose, MERS-CoV neutralising antibodies were highest for participants assigned to 56-day 10$ PFU, with geometric mean ratios of 7.2 (95% CI 3.9-13.3) for the 56-day 10$ PFU group versus the 28-day 10$ PFU group (p<0<middle dot>0001), 3.9 (2.1-7.2) for the 56-day 10$ PFU group versus the 56-day 107 PFU group (p=0.0031), and 5.4 (2.9-10.0) for the 56-day 10$ PFU group versus the 28-day 107 PFU group (p=0.0003). Interpretation MVA-MERS-S was safe and immunogenic in individuals with previous and concurrent SARS-CoV-2 exposure. The second vaccination with the 10$ PFU dose of MVA-MERS-S elicited a stronger humoral immune response when administered 56 days after the first dose than a 28-day interval. Further studies are needed to verify these findings in groups at risk for MERS-CoV exposure, and at risk of severe disease, including older individuals and those with relevant comorbidities. Funding Coalition for Epidemic Preparedness Innovations, the German Centre for Infection Research, and the German Research Foundation.Copyright (c) 2024 Elsevier Ltd. All rights reserved, including those for text and data mining, AI training, and similar technologies.