The effect of dose on the safety and immunogenicity of the VSV Ebola candidate vaccine: a randomised double-blind, placebo-controlled phase 1/2 trial

Abstract

Background: Safe and effective vaccines against Ebola could prevent or control outbreaks. The safe use of replication-competent vaccines requires a careful dose-selection process. We report the first safety and immunogenicity results in volunteers receiving 3 × 10(5) plaque-forming units (pfu) of the recombinant vesicular stomatitis virus-based candidate vaccine expressing the Zaire Ebola virus glycoprotein (rVSV-ZEBOV; low-dose vaccinees) compared with 59 volunteers who had received 1 ×10(7) pfu (n=35) or 5 × 10(7) pfu (n=16) of rVSV-ZEBOV (high-dose vaccinees) or placebo (n=8) before a safety-driven study hold.

Methods: The Geneva rVSV-ZEBOV study, an investigator-initiated phase 1/2, dose-finding, placebo-controlled, double-blind trial conducted at the University Hospitals of Geneva, Switzerland, enrolled non-pregnant, immunocompetent, and otherwise healthy adults aged 18-65 years. Participants from the low-dose group with no plans to deploy to Ebola-aff5cted regions (non-deployable) were randomised 9:1 in a double-blind fashion using randomly permuted blocks of varying sizes to a single injection of 3 × 10(5) pfu or placebo, whereas deployable participants received single-injection 3 × 10(5) pfu open-label. Primary safety and immunogenicity outcomes were the incidence of adverse events within 14 days of vaccination and day-28 antibody titres, respectively, analysed by intention to treat. After viral oligoarthritis was observed in 11 of the first 51 vaccinees (22%) receiving 10(7) or 5 × 10(7) pfu, 56 participants were given a lower dose (3 × 10(5) pfu, n=51) or placebo (n=5) to assess the effect of dose reduction on safety and immunogenicity. This trial is ongoing with a follow-up period of 12 months; all reported results are from interim databases. This study is registered with ClinicalTrials.gov, number NCT02287480.

Findings: Between Jan 5 and Jan 26, 2015, 43 non-deployable participants received low-dose rVSV-ZEBOV (3 × 10(5) pfu) or placebo in a double-blind fashion, whereas 13 deployable participants received 3 × 10(5) pfu open-label. Altogether, in the low-dose group, 51 participants received rVSV-ZEBOV and five received placebo. No serious adverse events occurred. At 3 × 10(5) pfu, early-onset reactogenicity remained frequent (45 [88%] of 51 compared with 50 [98%] of 51 high dose and two [15%] of 13 placebo recipients), but mild. Objective fever was present in one (2%) of 51 low-dose versus 13 (25%) of 51 high-dose vaccinees receiving at least 1 ×10(7) pfu (p<0·0001). Subjective fever (p<0·0001), myalgia (p=0·036), and chills (p=0·026) were significantly reduced and their time of onset delayed, reflecting significantly lower viraemia (p<0·0001) and blood monocyte-activation patterns (p=0·0233). Although seropositivity rates remained similarly high (48 [94%] of 51), day-28 EBOV-glycoprotein-binding and neutralising antibody titres were lower in low-dose versus high-dose vaccinees (geometric mean titres 344·5 [95% CI 229·7-516·4] vs 1064·2 [757·6-1495·1]; p<0·0001; and 35·1 [24·7-50·7] vs 127·0 [86·0-187·6]; p<0·0001, respectively). Furthermore, oligoarthritis again occurred on day 10 (median; IQR 9-14) in 13 (25%) of 51 low-dose vaccinees, with maculopapular, vesicular dermatitis, or both in seven (54%) of 13; arthritis was associated with increasing age in low-dose but not high-dose vaccinees. Two vaccinees presented with purpura of the lower legs; histological findings indicated cutaneous vasculitis. The presence of rVSV in synovial fluid and skin lesions confirmed causality.

Interpretation: Reducing the dose of rVSV-ZEBOV improved its early tolerability but lowered antibody responses and did not prevent vaccine-induced arthritis, dermatitis, or vasculitis. Like its efficacy, the safety of rVSV-ZEBOV requires further definition in the target populations of Africa.

Funding: Wellcome Trust through WHO.

Figure 1. Trial profile

14 (10%) of 142 participants were excluded or withdrawn before study intervention due to ineligibility and 13 (9%) of 142 withdrew during the study hold. *The deployable participant and one non-deployable participant were withdrawn due to concerns regarding ability to follow the study protocol and the other non-deployable participant for uncontrolled hypertension just before the planned randomisation. rVSV-ZEBOV=recombinant vesicular stomatitis virus-based Zaire Ebola virus vaccine. pfu=plaque-forming units.

Figure 2. Comparison of local and systemic adverse events after receipt of rVSV-ZEBOV or placebo

Solicited adverse events reported in the first 14 days after injection and their severity are reported following injection of 3 × 10⁵ plaque-forming units (pfu; low dose, n=51), 1×10⁷ pfu or 5 × 10⁷ pfu (high dose, n=51), or placebo (n=13). p values for comparisons between low-dose and high-dose recipients (shown on the right) show a significant dose effect on pain, subjective and objective fever, and myalgia, with similar trends for chills, fatigue, and headaches. rVSV-ZEBOV=recombinant vesicular stomatitis virus-based Zaire Ebola virus vaccine.

Figure 3. Glycoprotein antibody titres by vaccine dose and assay

Individual antibody titres assessed at baseline and 28 days after injection by dose group. Results from high-dose vaccinees, previously reported, are provided for comparison. Antibodies were measured by ELISA against the homologous glycoprotein of Zaire-Kikwit strain (USAMRIID [A], ADI [B]) or inactivated whole virions of the Zaire-Makona strain (C). Data are geometric mean concentration of endpoint titres (A) or of AEUs per mL (B, C) with 95% CIs. The shaded zones indicate the quantification thresholds. Neutralising antibodies were detected with rVSV pseudovirions complemented by homologous glycoprotein (D). Geometric mean titres and 95% CIs are shown for each dose group and timepoint assessed. The shaded zone indicates the quantification threshold. The results of USAMRIID glycoprotein-ELISA (E) and pseudovirion neutralisation assay (F) were expressed as the reciprocal of the highest dilution showing a positive result. The curves represent the distribution of individual antibody titres in each dose group. Dotted lines indicated baseline titres (E). USAMRIID=US Army Medical Research Institute of Infectious Diseases. ADI=Alpha Diagnostic International. EU=ELISA units. AEU=arbitrary ELISA units. PsVNA50=pseudovirion neutralisation assay. pfu=plaque-forming units. ZEBOV-GP=Zaire Ebola virus glycoprotein.

Figure 4. Cutaneous vasculitis after rVSV-ZEBOV immunisation

Purpuric lesions on the pretibial area (A) and lower legs (D) of two vaccinees. Haematoxylin and eosin stain (original magnification × 2) shows swollen endothelial cells and a dense perivascular lymphocytic infiltrate with numerous extravasated erythrocytes, but no fibrinoid necrosis or thrombi (B, E). Examination of skin biopsy samples were done on days 2 and 5 after the onset of purpura, respectively. Immunostaining identifies the lymphocytic infiltrate as composed mainly of CD4+ T cells (C, F). Complement C3 was detected in the vessel walls and at the dermal epidermal junction (not shown), without IgG, IgM, or IgA deposits. rVSV-ZEBOV=recombinant vesicular stomatitis virus-based Zaire Ebola virus vaccine.