Ebola Vaccine Long-Term Safety and Antibody Response

An Ebola virus vaccine produced long-term antibody responses for up to 1 year with few adverse events, according to a study published in the Lancet Infectious Diseases.¹

At this time, there is no licensed vaccine for Ebola virus disease. Ever since the outbreak of Ebola in west Africa in 2013-2016, the recombinant vesicular stomatitis virus-Zaire Ebola virus envelope glycoprotein vaccine (rVSVΔG-ZEBOV-GP) has been investigated as a promising candidate for a safe and effective vaccine.²

The Guinea ring vaccination study, a phase 3 trial, showed that rVSVΔG-ZEBOV-GP provided 100% protection against Ebola 10 days after vaccine administration among individuals living in West Africa during the outbreak. Adverse events were mild, and serious adverse events were rare.² However, because participants were only followed-up for 84 days, long-term safety and efficacy data for rVSVΔG-ZEBOV-GP are lacking.^1,2

To address this issue, researchers evaluated the immunogenicity and safety of rVSVΔG-ZEBOV-GP over the course of 1 year in healthy adults in a phase 1 study.¹

A total of 512 participants were enrolled and received the assigned immunization. Cohort 1 had 330 participants who were randomly assigned to a single intramuscular injection of rVSVΔG-ZEBOV-GP (3×10³, 3×10⁴, 3×10⁵, or 3×10⁶ plaque-forming units [PFUs] doses) or placebo. Cohort 2 included 182 participants randomly assigned to rVSVΔG-ZEBOV-GP (3×10⁶, 9×10⁶, 2×10⁷, or 1×10⁸ PFU doses) or placebo. A total of 488 participants completed the study through day 360.¹

Most participants had onset of antibody response by day 14 and exhibited immune responses by day 28. Higher doses elicited a more robust immune response, as measured by immunoglobulin G ELISA titers and 60% plaque-reduction neutralization test (PRNT60) titers, than lower doses (P =.0003 and P <.0001, respectively).¹

However, participants receiving the 2×10⁷ PFU dose, which was evaluated in the Guinea ring study, had similar IgG ELISA and PRNT60 titers as patients receiving the highest dose (P =.770 and P =.202, respectively). Seroconversion, as measured by geometric mean IgG ELISA and PRNT60 titers, occurred in 95.7% of participants receiving the 2×10⁷ PFU dose by day 28, and high rates of seroconversion were maintained through day 360.¹

Most adverse events were mild or moderate, occurred within 1 day of vaccination, and were more frequent with higher vaccine doses. The most common adverse events with the 2×10⁷ PFU dose that was used in phase 3 trials included headache, fatigue, and myalgia. Postvaccination arthritis and dermatitis were self-limited and occurred in 4.5% and 5.7% of participants, respectively.¹

“This well-conducted study extends our knowledge base about the Ebola vaccine, which was shown in the Guinea ring study to offer 100% protection. Here, we learn that the antibody responses are long-lasting and persist for 1 year in this study, and it is likely that they persist for much longer. General safety of this Ebola vaccine is again shown, with a low incidence of arthritis and dermatitis,” Mark J. Mulligan, MD, executive director of the Hope Clinic of the Emory Vaccine Center in Decatur, Georgia, told Infectious Disease Advisor.

Dr Mulligan also added that these findings “will add to the safety and immune response data that regulatory bodies will review for approval.”

According to Dr Mulligan, however, questions still remain regarding the effects of rVSVΔG-ZEBOV-GP in humans. “The study reports only the antibody response, but not T-cell responses. We still don’t know what the correlate of protection is in humans, and we also don’t know the minimum protective dose,” he said.

Reference

1. Heppner DG Jr, Kemp TL, Martin BK, et al; V920-004 study team. Safety and immunogenicity of the rVSV∆G-ZEBOV-GP Ebola virus vaccine candidate in healthy adults: a phase 1b randomised, multicentre, double-blind, placebo-controlled, dose-response study [published online June 9, 2017]. Lancet Infect Dis. doi: 10.1016/S1473-3099(17)30313-4
2. Henao-Restrepo AM, Camacho A, Longini IM, et al. Efficacy and effectiveness of an rVSV-vectored vaccine in preventing Ebola virus disease: final results from the Guinea ring vaccination, open-label, cluster-randomised trial (Ebola Ça Suffit!). Lancet. 2017;389(10068):505-518. doi: 10.1016/S0140-6736(16)32621-6