Safety and immunogenicity of a skin- and neuro-attenuated live vaccine for varicella: a randomized, double-blind, controlled, dose-escalation and age de-escalation phase 1 clinical trial

Background Despite the success in decreasing varicella-related disease burden, live-attenuated Oka vaccine strain of varicella-zoster virus (vOka) remains neuro-virulence and may establish latency and reactivate, raising safety concerns. Here we aimed to evaluate the safety and immunogenicity of a skin-and neuro-attenuated varicella vaccine candidate (v7D).Methods This is a randomized, double-blind, placebo-controlled, dose-escalation and age de-escalation phase 1 clinical trial conducted in Liuzhou, China (ChiCTR1900022284). Eligible healthy participants aged 1-49 years, with no history of varicella vaccination and had no history of varicella or herpes zoster were sequentially enrolled and allocated to subcutaneously receive one of the three doses (3.3, 3.9, and 4.2 lg PFU) of v7D, vOka or placebo in a dose-escalation and age de-escalation manner. The primary outcome was safety, assessed by adverse events/ reactions within 42 days after vaccination and serious adverse events (SAEs) throughout six months after vaccination. The secondary outcome was immunogenicity, assessed by the VZV IgG antibodies measured with fluorescent antibody to membrane antigen (FAMA) assay.Findings Between April 2019 and March 2020, totally 224 participants were enrolled. Within 42 days post-vaccination, the incidences of adverse reactions were 37.5%-38.7% in the three doses of v7D groups which were similar to that of the vOka (37.5%) and placebo (34.4%) groups. No SAE has been judged as causally related to vaccination. At 42 days post-vaccination, 100% of children aged 1-12 years in the per-protocol set of immunogenicity cohort of the v7D groups became seropositive. Meanwhile, in the intent-to-treat set of immunogenicity cohort of subjects aged 1-49 years, the geometric mean increases of the three groups of v7D vaccine were 3.8, 5.8 and 3.2, respectively, which were similar to that of the vOka vaccine group (4.4) and significantly higher than that of the placebo group (1.3). Interpretation The candidate v7D vaccine has been preliminarily shown to be well-tolerated and immunogenic in humans. The data warrant further evaluation of the safety advantage and efficacy of v7D as a varicella vaccine.