Safety and immunogenicity of a trivalent virus-like particle vaccine against western, eastern, and Venezuelan equine encephalitis viruses: a phase 1, open-label, dose-escalation, randomised clinical trial

Abstract

Background: Western (WEEV), eastern (EEEV), and Venezuelan (VEEV) equine encephalitis viruses are mosquito-borne pathogens classified as potential biological warfare agents for which there are currently no approved human vaccines or therapies. We aimed to evaluate the safety, tolerability, and immunogenicity of an investigational trivalent virus-like particle (VLP) vaccine, western, eastern, and Venezuelan equine encephalitis (WEVEE) VLP, composed of WEEV, EEEV, and VEEV VLPs.

Methods: The WEVEE VLP vaccine was evaluated in a phase 1, randomised, open-label, dose-escalation trial at the Hope Clinic of the Emory Vaccine Center at Emory University, Atlanta, GA, USA. Eligible participants were healthy adults aged 18-50 years with no previous vaccination history with an investigational alphavirus vaccine. Participants were assigned to a dose group of 6 μg, 30 μg, or 60 μg vaccine product and were randomly assigned (1:1) to receive the WEVEE VLP vaccine with or without aluminium hydroxide suspension (alum) adjuvant by intramuscular injection at study day 0 and at week 8. The primary outcomes were the safety and tolerability of the vaccine (assessed in all participants who received at least one administration of study product) and the secondary outcome was immune response measured as neutralising titres by plaque reduction neutralisation test (PRNT) 4 weeks after the second vaccination. This trial is registered at ClinicalTrials.gov, NCT03879603.

Findings: Between April 2, 2019, and June 13, 2019, 30 trial participants were enrolled (mean age 32 years, range 21-48; 16 [53%] female participants and 14 [47%] male participants). Six groups of five participants each received 6 μg, 30 μg, or 60 μg vaccine doses with or without adjuvant, and all 30 participants completed study follow-up. Vaccinations were safe and well tolerated. The most frequently reported symptoms were mild injection-site pain and tenderness (22 [73%] of 30) and malaise (15 [50%] of 30). Dose-dependent differences in the frequency of pain and tenderness were found between the 6 μg, 30 μg, and 60 μg groups (p=0·0217). No significant differences were observed between dosing groups for any other reactogenicity symptom. Two adverse events (mild elevated blood pressure and moderate asymptomatic neutropenia) were assessed as possibly related to the study product in one trial participant (60 μg dose with alum); both resolved without clinical sequelae. 4 weeks after second vaccine administration, neutralising antibodies were induced in all study groups with the highest response seen against all three vaccine antigens in the 30 μg plus alum group (PRNT₈₀ geometric mean titre for EEEV 60·8, 95% CI 29·9-124·0; for VEEV 111·5, 49·8-249·8; and for WEEV 187·9, 90·0-392·2). Finally, 4 weeks after second vaccine administration, for all doses, the majority of trial participants developed an immune response to all three vaccine components (24 [83%] of 29 for EEEV; 26 [90%] of 29 for VEEV; 27 [93%] of 29 for WEEV; and 22 [76%] of 29 for EEEV, VEEV, and WEEV combined).

Interpretation: The favourable safety profile and neutralising antibody responses, along with pressing public health need, support further evaluation of the WEVEE VLP vaccine in advanced-phase clinical trials.

Funding: The Vaccine Research Center of the National Institute of Allergy and Infectious Diseases, National Institutes of Health funded the clinical trial. The US Department of Defense contributed funding for manufacturing of the study product.

Figure 1:. VRC 313 Trial CONSORT Diagram.

Participants were enrolled according to a dose-escalation protocol and randomized within each dose group to receive two doses of WEVEE VLP with or without alum, eight weeks apart. One participant did not receive the second vaccination due to asymptomatic neutropenia but continued with safety follow-up. All participants completed at least 12 weeks of follow-up.

Figure 2:. Maximum local and systemic solicited reactogenicity.

Percent of participants (x-axis) who reported a local or systemic symptom (y-axis) in the seven days following administration of vaccination 1 (study week 0) and vaccination 2 (study week 8). There were no reported local symptoms of redness or swelling, or systemic symptom of fever for any participants following either vaccination, n = 5 for all dose groups except for 6 mcg WEVEE (n = 4) following vaccination 2.

Figure 3:. Neutralizing Antibodies.

PRNT₈₀ titers for EEEV (Panel A), VEEV (Panel B), and WEEV (Panel C) at baseline (Pre) and at 4, 16, and 24 weeks post the second product administration are shown. Participants received 6, 30, or 60 mcg WEVEE VLP without alum (open circles) or with alum (closed circles). The reciprocal of the serum dilution which neutralizes 80% of the input virus are shown as PRNT₈₀ titers for each participant. A positive response was defined as a PRNT₈₀ value ≥ 10 as indicated by the dotted horizontal line. A two-sample t-test was used to compare groups, and statistically significant p values (<0·05) are shown. Both dose- and alum-dependent responses are observed, and positive responses are seen in nearly all participants in the 30 and 60 mcg dose groups with and without alum. Highest responses are seen in the 30mcg + alum group against all three viruses at week 4 post second vaccine administration.

Figure 4:. Durability of Neutralizing Antibody Response.

PRNT₈₀ titers for EEEV (Panel A), VEEV (Panel B), and WEEV (Panel C) up to 28 weeks post second product administration. Participants received 6, 30, or 60 mcg WEVEE VLP without alum (open circles) or with alum (closed circles) administered at day 0 and study week 8 indicated by black arrows. The reciprocal of the serum dilution which neutralizes 80% of the input virus is shown as the geometric mean PRNT₈₀ titers by study group, with 95% confidence intervals indicated by error bars. A positive response was defined as a PRNT₈₀ value ≥ 10 as indicated by dotted horizontal line, and n = 5 for all dose groups with the exception of 6 mcg WEVEE (n = 4). Peak neutralizing responses were seen at 2 weeks (EEEV, VEEV) and 4 weeks (WEEV) post second vaccination. The dosing effect is observed out to the last study time point, and an alum-dependent response is seen in the 6 and 30 mcg dosing groups throughout the study time course.