• Nadine C Salisch, Kathryn E Stephenson, Kristi Williams, Freek Cox, Leslie van der Fits, Dirk Heerwegh, Carla Truyers, Marrit N Habets, Diane G Kanjilal, Rafael A Larocca, Peter Abbink, Jinyan Liu, Lauren Peter, Carlos Fierro, Rafael A De La Barrera, Kayvon Modjarrad, Roland C Zahn, Jenny Hendriks, Conor P Cahill, Maarten Leyssen, Macaya Douoguih, Johan van Hoof, Hanneke Schuitemaker, and Dan H Barouch.
• Janssen Vaccines and Prevention, Leiden, the Netherlands (N.C.S., F.C., L.V., M.N.H., R.C.Z., J.H., C.P.C., M.L., M.D., J.V., H.S.).
• Ann. Intern. Med. 2021 May 1; 174 (5): 585-594.

BackgroundZika virus (ZIKV) may cause severe congenital disease after maternal-fetal transmission. No vaccine is currently available.ObjectiveTo assess the safety and immunogenicity of Ad26.ZIKV.001, a prophylactic ZIKV vaccine candidate.DesignPhase 1 randomized, double-blind, placebo-controlled clinical study. (ClinicalTrials.gov: NCT03356561).SettingUnited States.Participants100 healthy adult volunteers.InterventionAd26.ZIKV.001, an adenovirus serotype 26 vector encoding ZIKV M-Env, administered in 1- or 2-dose regimens of 5 × 1010 or 1 × 1011 viral particles (vp), or placebo.MeasurementsLocal and systemic adverse events; neutralization titers by microneutralization assay (MN50) and T-cell responses by interferon-γ enzyme-linked immunospot and intracellular cytokine staining; and protectivity of vaccine-induced antibodies in a subset of participants through transfer in an exploratory mouse ZIKV challenge model.ResultsAll regimens were well tolerated, with no safety concerns identified. In both 2-dose regimens, ZIKV neutralizing titers peaked 14 days after the second vaccination, with geometric mean MN50 titers (GMTs) of 1065.6 (95% CI, 494.9 to 2294.5) for 5 × 1010 vp and 956.6 (595.8 to 1535.8) for 1 × 1011 vp. Titers persisted for at least 1 year at a GMT of 68.7 (CI, 26.4-178.9) for 5 × 1010 vp and 87.0 (CI, 29.3 to 258.6) for 1 × 1011 vp. A 1-dose regimen of 1 × 1011 vp Ad26.ZIKV.001 induced seroconversion in all participants 56 days after the first vaccination (GMT, 103.4 [CI, 52.7 to 202.9]), with titers persisting for at least 1 year (GMT, 90.2 [CI, 38.4 to 212.2]). Env-specific cellular responses were induced. Protection against ZIKV challenge was observed after antibody transfer from participants into mice, and MN50 titers correlated with protection in this model.LimitationThe study was conducted in a nonendemic area, so it did not assess safety and immunogenicity in a flavivirus-exposed population.ConclusionThe safety and immunogenicity profile makes Ad26.ZIKV.001 a promising candidate for further development if the need reemerges.Primary Funding SourceJanssen Vaccines and Infectious Diseases.

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