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Self-replicating RNA (srRNA) technology, in comparison to mRNA vaccines, has shown dose-sparing by approximately 10-fold and more durable immune responses. However, no improvements are observed in the adverse events profile. Here, we develop an srRNA vaccine platform with optimized non-coding regions and demonstrate immunogenicity and safety in preclinical and clinical development. Optimized srRNA vaccines generate protective immunity (according to the WHO defined thresholds) at doses up to 1,000,000-fold lower than mRNA in female mouse models of influenza and rabies. Clinically, safety and immunogenicity of RBI-4000, an srRNA vector encoding the rabies glycoprotein, was evaluated in a Phase I study (NCT06048770). RBI-4000 was able to elicit de novo protective immunity in the majority of healthy participants when administered at a dose of 0.1, 1, or 10 microgram (71%, 94%, 100%, respectively) in a prime-boost schedule. Similarly, we observe immunity above the WHO benchmark of protection following a single administration in most participants at both 1 and 10 microgram doses. There are no serious adverse events reported across all cohorts. These data establish the high therapeutic index of optimized srRNA vectors, demonstrating feasibility of both low dose and single dose approaches for vaccine applications. Here the authors report an optimized self-replicating RNA (srRNA) vaccine approach that generates protective immunity at much lower doses than mRNA vaccines in mice. In a Phase 1 study using rabies glycoprotein as antigen, they show robust immune responses at doses as low as 0.1 µg, with a favorable safety profile.

•SYN023-004: a large, one-year, randomized, double blind, controlled, rabies PEP study in Category III patients.•SYN023 is comprised of two humanized monoclonals against non-overlapping rabies virus epitopes.•SYN023 produces rapid and higher RVNA during the 2-week period after administration.•SYN023 safety profile appears similar to human rabies immunoglobulin. SYN023 is an anti-rabies monoclonal antibody mixture administered as part of post-exposure prophylaxis regimens. The rabies virus neutralizing antibody (RVNA) concentration generally accepted as an adequate immune response to vaccination is ≥ 0.5 IU/mL. Within 54 h of potential rabies exposure, 448 patients in two risk substrata of WHO Category III exposure were randomized to receive either 0.3 mg/kg SYN023 or 0.133 mL/kg human rabies immunoglobulin (HRIG) injected in and around the wound site(s) plus a course of rabies vaccination. Patients were followed for safety and absence of rabies for ≥ 365 days. GMT RVNA was higher with SYN023 throughout the 2-week post-treatment period. In the primary analysis group (n = 368), 99.4 % of SYN023 recipients versus 4.5 % of HRIG recipients had protective RVNA levels on Day 4. On Day 8, 98.1 % SYN023 versus 12.2 % HRIG recipients were protected. The SYN023:HRIG ratio of geometric mean titer of RVNA (RVNA GMTs) on Day 8 (19.42) exceeded the 10 % superiority margin (P < 0.0001) indicating higher Day 8 RVNA with SYN023. On Day 99, the SYN023:HRIG RVNA GMT ratio (0.66) was below the non-inferiority margin of 20 % (P = 0.9485) suggesting some moderation of vaccine immune response by SYN023 relative to HRIG. The ratio of percent SYN023:HRIG recipients achieving RVNA ≥ 0.5 IU/mL on Day 99 (0.98) met the non-inferiority margin of 20 % (P = 0.013) indicating anti-rabies immune response with SYN023 was non-inferior to HRIG despite this effect. There were no probable/confirmed rabies cases in any patient. Study regimens were well tolerated. SYN023 provided higher RVNA than HRIG soon after rabies exposure. By Day 99 post-treatment, GM RVNA with SYN023 was lower than HRIG, however, the percent of SYN023 recipients with a protective response was not inferior at this time point. No rabies cases were reported in the study. The SYN023 safety profile was acceptable. ClinicalTrials.gov ID: NCT03961555.

Tens of thousands of people die from dog-mediated rabies annually. Deaths can be prevented through post-exposure prophylaxis for people who have been bitten, and the disease eliminated through dog vaccination. Current post-exposure prophylaxis use saves many lives, but availability remains poor in many rabies-endemic countries due to high costs, poor access, and supply. We developed epidemiological and economic models to investigate the effect of an investment in post-exposure prophylaxis by Gavi, the Vaccine Alliance. We modelled post-exposure prophylaxis use according to the status quo, with improved access using WHO-recommended intradermal vaccination, with and without rabies immunoglobulin, and with and without dog vaccination. We took the health provider perspective, including only direct costs. We predict more than 1 million deaths will occur in the 67 rabies-endemic countries considered from 2020 to 2035, under the status quo. Current post-exposure prophylaxis use prevents approximately 56 000 deaths annually. Expanded access to, and free provision of, post-exposure prophylaxis would prevent an additional 489 000 deaths between 2020 and 2035. Under this switch to efficient intradermal post-exposure prophylaxis regimens, total projected vaccine needs remain similar (about 73 million vials) yet 17·4 million more people are vaccinated, making this an extremely cost-effective method, with costs of US$635 per death averted and $33 per disability-adjusted life-years averted. Scaling up dog vaccination programmes could eliminate dog-mediated rabies over this time period; improved post-exposure prophylaxis access remains cost-effective under this scenario, especially in combination with patient risk assessments to reduce unnecessary post-exposure prophylaxis use. Investing in post-exposure vaccines would be an extremely cost-effective intervention that could substantially reduce disease burden and catalyse dog vaccination efforts to eliminate dog-mediated rabies. World Health Organization.

The aim of this study is to demonstrate that the freeze-dried human rabies vaccine (Vero cell), administered in a four-dose schedule (2-1-1) to the 10–60 years old population, has immunogenicity that is not inferior to the approved five-dose schedule and similar vaccines with a four-dose schedule, and to evaluate its safety. A total of 1800 individuals were enrolled and divided into three groups: four-dose test group, four-dose control group, and five-dose control group. The rabies virus neutralizing antibodies were measured using the Rapid Fluorescent Focus Inhibition Test to assess immunogenicity, and the incidence of adverse events and serious adverse events were statistically analyzed. The seroconversion rates 14 days after the first dose and 14 days after the complete course of vaccination were 100% in all three groups. The antibody GMC of the four-dose test group was higher than that of the five-dose control group, but slightly lower than the four-dose control group. Seven days after the first dose, both four-dose regimen groups showed higher seroconversion rates and antibody GMCs compared to the five-dose regimen group, proving that the immunogenic effect of the four-dose regimen seven days post-first vaccination is superior to the five-dose regimen. The overall incidence of adverse events showed no significant difference between the four-dose test group and the five-dose control group, but was significantly lower in the four-dose test group compared to the four-dose control group. The vaccine in the four-dose test group is equivalent in immunogenic effect to the four-dose control group vaccine and superior to the five-dose control group vaccine; the safety of the vaccine in the four-dose test group is equivalent to the five-dose control group vaccine and superior to the four-dose control group vaccine. clinicaltrials.gov number: NCT05549908.

To evaluate the safety, immunogenicity and immune persistence of a lyophilized purified human diploid cells rabies vaccine in healthy and previously unvaccinated people in a simulated rabies post-exposure prophylaxis, by traditional 5-dose Essen regimen and abbreviated 4-dose Zagreb regimen. A cohort of 1800 healthy participants aged 10–60 years old were randomized into three groups: 5-dose test group (T5, Essen regimen), 5-dose control group (C5, Essen regimen) and 4-dose test group (T4, Zagreb regimen) according to the ratio of 1:1:1, and inoculated with trial vaccine or control vaccine separately to analyze the safety of vaccine as well as rabies antibody levels before and after vaccination. Adverse reactions (AEs) mainly occurred after the initial dose of immunization, which were mostly mild (grade 1) in severity. The incidence of total AEs in T4 (38 %) was lower than that in C5 (45 %) (P = 0.02) from the initial dose to 28 days after the final dose; fever rate in T5 (12 %, P = 0.01) and T4 (13 %, P = 0.03) was lower than that in C5 (17 %). No vaccine-related serious AEs (SAEs) were observed. Seroconversion rates reached 100 % in all three groups 14 days following the first dose. Moreover, the seroconversion rate was 98 %, 96 % and 98 % 12 months following the first dose in T5, C5 and T4, respectively. Both T5 and T4 displayed higher neutralizing antibodies geometric mean concentration (GMC) and geometric mean increase (GMI) compared to those in C5 on day 7, day 14, and 12 months after the first dose, as well as on day 14 after the last dose. There were no significant differences in the incidence of AEs, seroconversion rate, GMC and GMI between T5 and T4. The trial vaccine administered following both Essen regimen and Zagreb regimen shows good safety, immunogenicity and immune persistence, and the trial vaccine is not inferior to the control vaccine. Clinical Trials Registration:NCT03971370.

Rabies is almost invariably fatal. A rabies monoclonal antibody (RmAb) was approved in India in 2016 for passive prophylaxis. This post-marketing study aimed to evaluate the long-term safety, immunogenicity, and efficacy of a post-exposure prophylaxis (PEP) regimen containing RmAb. This phase 4, open-label, randomised, active-controlled study was conducted at 15 tertiary care hospitals in India. Patients aged 2 years or older with WHO category 3 rabies exposure by a suspected rabid animal were eligible if the exposure occurred less than 72 h before enrolment, or less than 24 h before enrolment for exposures to the face, neck, hand, or fingers. Participants were randomly assigned (3:1) to receive either RmAb (Rabishield; Serum Institute of India, Pune, India) plus a purified Vero cell rabies vaccine (PVRV; Rabivax-S) or equine rabies immunoglobulin (ERIG; Equirab) plus PVRV as PEP. In each treatment group, patients were further randomly assigned (1:1) to receive PVRV either intradermally or intramuscularly. Study group allocation was done using a permuted block design with random block sizes of eight. A central randomisation list was generated before the study start and randomisation was performed with an interactive web response system. Participants and site personnel were not masked to group assignment. RmAb (3·33 IU/kg) and ERIG (40 IU/kg) were infiltrated into and around the wounds only on day 0 as per WHO 2018 recommendations. PVRV was administered 1·0 mL intramuscularly (days 0, 3, 7, 14, and 28) or 0·1 mL plus 0·1 mL intradermally (days 0, 3, 7, and 28). The primary outcome was treatment-related serious adverse events up to 365 days after immunisation, analysed in the safety analysis set (all participants who received at least one dose of vaccine with treatment). Geometric mean concentrations of rabies virus neutralising antibody were measured in a subset of patients. This study is registered with Clinical Trial Registry–India (CTRI/2019/06/019622) and is completed. 4059 participants were enrolled between Aug 21, 2019, and March 31, 2022, and randomly assigned. A total of 3994 participants (3001 male, 993 female) were treated (2996 RmAb plus PVRV, 998 ERIG plus PVRV), of which 3622 (90·7%) participants completed the 1-year follow-up. 11 adverse events were considered causally related to RmAb plus PVRV and 17 were considered causally related to the ERIG plus PVRV regimen. Most adverse events were mild and transient. Seven serious adverse events occurred in the RmAb group and all were causally unrelated. One causally related serious adverse event was reported in the ERIG group. On day 14, the geometric mean concentrations increased to 16·05 IU/mL (95% CI 13·25–19·44) in the RmAb group and 13·48 IU/mL (9·51–19·11) in the ERIG group (point estimate 1·19 [95% CI 0·82–1·72]). No patient developed rabies during the 1-year follow-up period. RmAb was safe and well tolerated and showed protective efficacy against rabies. A PEP regimen containing RmAb plus PVRV was immunogenic with long-term persistence of immune response. Serum Institute of India.

The SYN023–006 study was conducted in WHO Category III rabies-exposed patient populations to assess the safety and efficacy of post-exposure prophylaxis that included either the monoclonal antibody mixture SYN023 or human rabies immunoglobulin (HRIG). This phase 3, double-blind, randomized, controlled trial was conducted at multiple clinical disease control sites in China. Patients were randomized 3:1 (stratified by study site) to wound infiltration with 0.3 mg/kg SYN023 or 20 IU/kg HRIG. All patients received thorough wound washing and 5 doses intramuscular Vero cell rabies vaccine. The composite primary study objective was to demonstrate: 1) superiority of Day 8 geometric mean (GM) concentration of serum rabies virus neutralizing antibodies (RVNA) with SYN023 versus HRIG (protocol-defined superiority margin: GM RVNA ratio 95 % confidence interval [CI] lower limit >1.2) and 2) no rabies in SYN023 recipients. Efficacy was evaluated in the Per-Protocol population. Safety endpoints included solicited and unsolicited adverse events (AEs) analyzed in all patients receiving any study treatment. Trial registration: ClinicalTrials.govNCT04644484. From 23 September 2020 to 26 June 2021, 537 male and 463 female patients were randomized (n = 750 SYN023, n = 250 HRIG). Day 8 GM RVNA was 4.339 IU/mL (standard error [SE]: 1.035) with SYN023 and 0.232 IU/mL (SE: 1.060) with HRIG. The SYN023:HRIG GM RVNA ratio was 18.695 (95 % CI: 16.440, 21.260) indicating superior RVNA with SYN023. No suspected rabies cases or deaths occurred. AEs were generally similar between treatment groups except greater local solicited AEs frequencies with HRIG (SYN023: 165/750 patients [22.0 %]; HRIG: 97/250 [38.8 %]). This study indicates that SYN023, a monoclonal antibody product, may be used as part of rabies post-exposure prophylaxis and provides superior protection sooner after exposure than HRIG.

The Zagreb and Essen regimens are comparable in terms of immunogenicity; however, how these regimens impact the immunogenicity of booster vaccination remains unknown. We conducted a clinical trial to assess the immunogenicity of booster vaccination with a purified Vero cell rabies vaccine after primary vaccination with the Zagreb or Essen regimens. This randomized, open-label, controlled, phase 3 trial, conducted in Shangyu City and Shengzhou City, Zhejiang Province, China, was divided into the primary and booster vaccination phases. After screening, all eligible participants were allocated to groups A, B, C, D, E, or F. Groups A, B, and C received the Zagreb regimen as the primary vaccine, while groups D, E, and F received the Essen regimen. The booster vaccination was conducted 6 months after the primary vaccination. Groups B and E received one dose of the booster, while groups C and F received two doses. Blood samples were collected before the booster, at 14 days after the booster, and at approximately 6 months after the booster. Safety was assessed from the first booster dose to 6 months after the final dose. A total of 718 participants completed the booster vaccination. The antibody positive rate (APR) of groups B, C, E, and F after the booster was 100%. The antibody titer rose significantly even after one booster, and was much higher in groups B (48.80 IU/ml) and C (64.38 IU/ml) (receiving Zagreb) than in groups E (34.25 IU/ml) and F (42.89 IU/ml) (receiving Essen). Although the incidence of ARs was higher in groups B (11.22%) and C (15.79%) than in groups E (3.68%) and F (10.87%), they were all mild and short-lived. No serious adverse events (SAEs) associated with vaccination were reported. The immunogenicity of booster vaccination after the Zagreb regimen was significantly higher than that after the Essen regimen. One booster may be sufficient to raise the antibody titer above the 0.5 IU/mL target. Clinical trial registration: This trial is registered at http://www.chinadrugtrials.org.cn/index.html under the registration number CTR20210426 at 08/03/2021.

Rabies pre-exposure prophylaxis (PrEP) is recommended to individuals at risk for exposure to rabies. Three intramuscular doses of the purified chick embryo cell (PCEC) rabies vaccine can be administered according to a conventional (four-week) or an accelerated (one-week) regimen. This phase III, open-label study (NCT02545517) was an extension of the NCT01662440 study where immune responses of different primary PrEP regimens with PCEC rabies vaccine and Japanese encephalitis (JE) vaccine were assessed. Adults who had completed the parent study and received three doses of rabies PrEP regimens, concomitantly with a JE vaccine or alone (i.e., Rabies+JE-Accelerated, Rabies+JE-Conventional, and Rabies-Conventional groups) were enrolled in this extension study. Here we evaluated the long-term (up to 10 years after completing the primary vaccination) immunogenicity and boostability of PCEC rabies vaccine, and the safety of booster dose(s). Immunogenicity was assessed in terms of rabies virus neutralizing antibody (RVNA) concentrations, and titers ≥0.5 international units (IU)/mL were considered adequate for protection. Participants with RVNA concentrations <0.5 IU/mL were eligible for receiving PCEC rabies vaccine booster(s). Of the 459 participants enrolled in this study, 77.6% completed the trial. At the study end, the probability of detecting adequate RVNA concentrations in unboosted participants was 57.8%, 60.2%, and 62.0% for the Rabies+JE-Accelerated, Rabies+JE-Conventional, and Rabies-Conventional groups, respectively. Overall, 68.6% of all participants had RVNA concentrations ≥0.5 IU/mL at any timepoint and did not require a booster dose during the study follow-up period. Of the 144 participants with RVNA concentrations <0.5 IU/mL at any timepoint, 132 needed one booster dose throughout the follow-up period (Years 3-10) and 12 needed multiple booster administrations. No safety concerns were identified. The PCEC rabies vaccine administered alone/concomitantly with the JE vaccine provides adequate immunity for up to 62% of unboosted participants at study end.

•Phase II study conducted comparing PIKA rabies vaccine accelerated regimen with standard rabies vaccine.•PIKA rabies vaccine is safe and well-tolerated.•PIKA rabies vaccine accelerated regimen is able to elicit protective immune response as early as Day 7.•All subjects in the PIKA group achieved protective RVNA titer by Day 14.•Immunogenicity of PIKA vaccine accelerated regimen is comparable to standard rabies vaccine. Human Rabies infection continues to be potentially fatal despite the availability of post-exposure prophylaxis with rabies vaccine. The PIKA Rabies vaccine adjuvant is a TLR3 agonist and has been shown to be safe and immunogenic in clinical phase I studies. We conducted a phase II, open label, randomized study in healthy adults to assess the safety and immunogenicity of the PIKA rabies vaccine under an accelerated regimen. 126 subjects were randomized into two groups: control vaccine classic regimen (“control-classic”) and PIKA vaccine accelerated regimen (“PIKA-accelerated”). Subjects were followed up for safety and rabies virus neutralizing antibodies (RVNA). Both the control and PIKA vaccines were generally well tolerated. 57.6% of subjects in the PIKA vaccine group, compared with 43.8% of subjects in the control-classic group, achieved the target RVNA titer of ≥0.5 IU/mL by Day 7. All subjects achieved the target RVNA titer by Day 14. The RVNA geometric mean titer at Day 7 was 0.60 IU/ml in the PIKA vaccine group and 0.39 IU/ml in the control-classic group. At Day 14, the RVNA geometric mean titer was 18.25 IU/ml in the PIKA-accelerated group and 19.24 IU/ml in the control-classic group. The median time taken to reach the target RVNA titer level of ≥0.5 IU/mL was 7.0 days (95% CI: 7.0–42.0 days) in the PIKA-accelerated group and 14.0 days (95% CI: 7.0–42.0 days) in the control-classic group. The accelerated regimen using the investigational PIKA Rabies vaccine was well-tolerated and demonstrated non-inferior immunogenicity compared to the classic regimen using the commercially available vaccine in healthy adults. Clinical trial registry: The study was registered with clinicaltrials.gov (NCT02956421).