First-in-Human Phase I Trial to Assess the Safety and Immunogenicity of an Orf Virus-Based COVID-19 Vaccine Booster

Abstract

The emergence of SARS-CoV-2 has necessitated the development of versatile vaccines capable of addressing evolving variants. Prime-2-CoV_Beta, a novel Orf virus-based COVID-19 vaccine, was developed to express the SARS-CoV-2 spike and nucleocapsid antigens. This first-in-human, phase I, dose-finding clinical trial was conducted to assess the safety, reactogenicity, and immunogenicity of Prime-2-CoV_Beta as a booster in healthy adults. From June 2022 to June 2023, 60 participants in Germany received varying doses of Prime-2-CoV_Beta. The study demonstrated a favorable safety profile, with no serious adverse events (AEs) reported. All AEs were mild (107) or moderate (10), with the most common symptoms being pain at the injection site, fatigue, and headache. Immunogenicity assessments revealed robust vaccine-induced antigen-specific immune responses. High doses notably elicited significant increases in antibodies against the spike and nucleocapsid proteins as well as neutralizing antibodies against SARS-CoV-2 and its variants. Additionally, the vaccine did not induce ORFV-neutralizing antibodies, indicating the potential for repeated administration. In conclusion, Prime-2-CoV_Beta was safe, well tolerated, and immunogenic, demonstrating potential as a broadly protective vaccine against SARS-CoV-2 and its variants. These promising results support further evaluation of higher doses and additional studies to confirm efficacy and long-term protection. This trial was registered at ClinicalTrials, NCT05389319.

Keywords: COVID-19; Orf virus; Parapoxvirus; SARS-CoV-2; first-in-human; immunogenicity; phase 1; safety; vaccine; viral vector.

Figure 1

Enrollment flow diagram. BMI = body mass index. PFU= plaque-forming units. TUE site = Institute of Tropical Medicine, University Hospital Tübingen. HH site = Bernhard Nocht Center for Clinical Trials, Hamburg.

Figure 2

Incidence of solicited local (A) and systemic (B) adverse events within the first 7 days following Prime-2-CoV_Beta vaccination. Day 1 represents the day of vaccination. AEs were categorized as mild (grade 1), moderate (grade 2), severe (grade 3), and life-threatening (grade 4). All AEs reported during this 7-day period are recorded.

Figure 2

Incidence of solicited local (A) and systemic (B) adverse events within the first 7 days following Prime-2-CoV_Beta vaccination. Day 1 represents the day of vaccination. AEs were categorized as mild (grade 1), moderate (grade 2), severe (grade 3), and life-threatening (grade 4). All AEs reported during this 7-day period are recorded.

Figure 3

Summary of solicited local and systemic adverse events following Prime-2-CoV_Beta vaccination. The number of participants who had reported solicited local and systemic AEs within 7 days post-immunization. AEs were categorized as mild (grade 1), moderate (grade 2), severe (grade 3), and life-threatening (grade 4). Each type of AE is counted only once per participant, and only the most severe occurrence is recorded. C1-C5 denotes the Cohorts 1–5, respectively.

Figure 4

SARS-CoV-2 spike- and nucleocapsid-specific antibody responses following Prime-2-CoV_Beta vaccination. IgG binding antibody levels against the S1 subunit of spike of the ancient SARS-CoV-2 (A), the RBD of spike of the ancient SARS-CoV-2 (B), the RBD of spike of the SARS-CoV-2 Beta variant (C), and of the nucleocapsid of the ancient SARS-CoV-2 (D) as measured in serum samples obtained from vaccinated participants at indicated time points by a validated in-house ELISA. Logarithmic values are reported as the geometric mean titer (GMT), and the bars represent the geometric mean with a 95% CI. Fold change from Day 29 to baseline is denoted above the columns. GMT at each time point is indicated in the columns. LLOQ = Lower Limit of Quantification is indicated by the dotted line. For pairwise comparisons of time points within each dose group, the Friedman test was used, followed by the Wilcoxon signed-rank test if the Friedman test was significant (p-value ≤ 0.05). * p < 0.05; ** p < 0.01.

Figure 4

SARS-CoV-2 spike- and nucleocapsid-specific antibody responses following Prime-2-CoV_Beta vaccination. IgG binding antibody levels against the S1 subunit of spike of the ancient SARS-CoV-2 (A), the RBD of spike of the ancient SARS-CoV-2 (B), the RBD of spike of the SARS-CoV-2 Beta variant (C), and of the nucleocapsid of the ancient SARS-CoV-2 (D) as measured in serum samples obtained from vaccinated participants at indicated time points by a validated in-house ELISA. Logarithmic values are reported as the geometric mean titer (GMT), and the bars represent the geometric mean with a 95% CI. Fold change from Day 29 to baseline is denoted above the columns. GMT at each time point is indicated in the columns. LLOQ = Lower Limit of Quantification is indicated by the dotted line. For pairwise comparisons of time points within each dose group, the Friedman test was used, followed by the Wilcoxon signed-rank test if the Friedman test was significant (p-value ≤ 0.05). * p < 0.05; ** p < 0.01.

Figure 5

SARS-CoV-2 neutralization response following Prime-2-CoV_Beta vaccination to ancestral SARS-CoV-2, Beta, Delta, and BA.5. Neutralizing antibody levels against the ancient SARS-CoV-2 (A), the SARS-CoV-2 Beta variant (B), the SARS-CoV-2 Delta variant (C), and the SARS-CoV-2 Omicron BA.5 variant (D) as measured in serum samples obtained from vaccinated participants at indicated time points by a validated microneutralization assay. Logarithmic values are reported as the GMT, and the bars represent the geometric mean with a 95% CI. Fold change from Day 29 to baseline is denoted above the columns. GMT at each time point is indicated in the columns. LLOQ = lower limit of quantification is indicated by the dotted line. For pairwise comparisons of time points within each dose group, the Friedman test was used, followed by the Wilcoxon signed-rank test if the Friedman test was significant (p-value ≤ 0.05).

Figure 5

SARS-CoV-2 neutralization response following Prime-2-CoV_Beta vaccination to ancestral SARS-CoV-2, Beta, Delta, and BA.5. Neutralizing antibody levels against the ancient SARS-CoV-2 (A), the SARS-CoV-2 Beta variant (B), the SARS-CoV-2 Delta variant (C), and the SARS-CoV-2 Omicron BA.5 variant (D) as measured in serum samples obtained from vaccinated participants at indicated time points by a validated microneutralization assay. Logarithmic values are reported as the GMT, and the bars represent the geometric mean with a 95% CI. Fold change from Day 29 to baseline is denoted above the columns. GMT at each time point is indicated in the columns. LLOQ = lower limit of quantification is indicated by the dotted line. For pairwise comparisons of time points within each dose group, the Friedman test was used, followed by the Wilcoxon signed-rank test if the Friedman test was significant (p-value ≤ 0.05).

Figure 6

ORFV-specific immune response and ORFV neutralization following Prime-2-CoV_Beta vaccination. IgG binding antibody levels (A) and neutralizing antibody levels (B) against ORFV strain D1701-VrV as measured in serum samples obtained from vaccinated participants at indicated time points by ELISA or microneutralization assay, respectively. Logarithmic values are reported as the GMT, and the bars represent the geometric mean with a 95% CI. Fold change from Day 29 to baseline is denoted above the columns. GMT at each time point is indicated in the columns. LLOQ = lower limit of quantification is indicated by the dotted line. For pairwise comparisons of time points within each dose group, the Friedman test was used, followed by the Wilcoxon signed-rank test if the Friedman test was significant (p-value ≤ 0.05). * p < 0.05; ** p < 0.01; *** p < 0.001.