Background and rationale: Geneva University Hospitals were granted a temporary authorization to administer the recombinant live vesicular stomatitis virus rVSV-ZEBOV (Ervebo®) vaccine to expatriate humanitarian frontline workers (FLWs) prior to mission deployment.

Objectives: Our aims were to assess the feasibility of FLW vaccination before deployment and to report adverse events (AEs).

Methods: FLWs received a single injection of rVSV-ZEBOV (>7.2E7 plaque forming unit) during their pre-deployment medical check-up at the Travel Medicine Clinic of the Geneva University Hospitals (Day 0). A safety questionnaire regarding potential AEs was emailed to FLWs on Days 3 and 21. Early and delayed AEs were those starting within 3 or 21 days of vaccination, respectively.

Results: Between 1 August 2019 and 30 June 2020, 124 FLWs received the rVSV-ZEBOV vaccine. Eighty-six volunteers (86/124; 69%) received a concomitant vaccine. The response rate to the follow-up questionnaire was 88 and 55% at Days 3 and 21, respectively. Most respondents (105/109; 96.3%), experienced at least one AE, with a mean of three (±SD 1.75) AEs per person. The most common AE was injection site pain, followed by fever (53/109; 48.6%), fatigue (51/109; 46.7%) and myalgia (49/109; 44.9%). Most early AEs (360/377; 95.4%) resolved within 3 days, reflecting vaccine reactogenicity. Delayed AEs were reported by 6/69 (7.2%) subjects, the median time to symptom onset was 11 days (range: 5-14); half of them were joint-related AEs (3/6). Four serious adverse events (SAE) were observed: two cases of high grade fever, one rash and one case of arthritis. Two suspected unexpected serious adverse reactions were observed: one case of continuing recurrent transient dizziness and fatigue considered related to the vaccine; and one case of presbyopia that was deemed unrelated.

Conclusion: AEs to rVSV-ZEBOV were common but in general transient and were well tolerated, pre-deployment rVSV-ZEBOV vaccination in FLW is feasible and can be included with pre-mission check-up.