Background: The Vero cell rabies vaccine is currently the most widely used human rabies vaccine. However, owing to the presence of residual host cell DNA (HCD) in the final product and the potential tumorigenicity of the DNA of high-passage Vero cells, the WHO not only sets a limit on the number of times cells used in production can be passaged, but also imposes strict requirements on the amount of residual HCD in the final vaccine product. Objectives: To systematically reduce the HCD level in the final vaccine product, multiple purification steps are included in the vaccine production process. This study investigated the effectiveness of key production steps in antigen recovery and DNA removal. Methods: The residual HCD fragment content and size distribution were detected using fluorescence quantitative PCR (qPCR) and capillary gel electrophoresis (CGE), and the rabies virus glycoprotein antigen content was detected using enzyme-linked immunosorbent assay (ELISA). The antigen recovery rate and HCD removal rate in each key process were calculated to evaluate the scientific basis and effectiveness of each production step. Additionally, the stability of the process was studied using multiple commercial batches of the product. Results: The results revealed that the total antigen recovery rate in the production process described in this report was no less than 8.5%, and the effective removal rate of residual HCD was not lower than 99.99%. Moreover, the amount of residual HCD in the final product was far below the quality standard of 2 ng/dose, and most of the residual HCD fragments were smaller than 200 bp. The results of the process stability studies on multiple commercial batches showed that the bulk human rabies vaccine produced by this process had excellent safety and efficacy and that the production process was stable and thus suitable for large-scale batch production. Conclusions: The production process described in this study achieved effective recovery of viral antigens and efficient removal of residual HCD, and the process was stable and controllable, enabling the continuous and stable production of vaccine products that meet WHO recommendations and the relevant requirements of the current edition of the Chinese Pharmacopeia. In addition, this study provides theoretical guidance for optimizing the vaccine production process.

Objectives: This study evaluated the 12-month persistence of rabies virus-neutralizing antibody (RVNA) following different immunization regimens of freeze-dried human rabies vaccine (Vero cells) in individuals aged 10–60 years within the Chinese population. Methods: Number of 600 participants from phase III clinical trials who completed the fullimmunization were randomly assigned into one of three groups, four-dose experimental group, five-dose experimental group, and five-dose control group. The experimental group received the vaccine from Shandong Yeedu Biotechnology Co., while the control group used the vaccine from Liaoning Chengda Biotechnology Co., Ltd. The antibody-positive rate and geometric mean concentration (GMC) were calculated, and analysis of variance was used to compare the results among the three groups. Results: The study included 200 participants in the four-dose experimental group, 186 in the five-dose experimental group, and 214 in the five-dose control group. Twelve months post-immunization, the overall RVNA-positive rates were 97.00%, 93.55%, and 94.86% in the four-dose experimental, five-dose control, and five-dose experimental groups, respectively. The GMCs of RVNA were 2.50, 2.05, and 2.04 IU/mL for the respective groups. The age-stratified analysis exhibited high positivity rates across age groups (≤21, 21–50, and ≥50), with rates ranging from 88.4% to 100%, and GMCs were between 1.75 and 2.61 IU/mL. Conclusions: Twelve months after full immunization, the overall RVNA-positive rate remained high across all dosing regimens, demonstrating satisfactory immunogenicity persistence. This indicates that both the four-dose and five-dose regimens are effective in maintaining long-term immunity against rabies.

Objective: In this paper, we aim to show that the immunogenicity of the lyophilized human rabies vaccine (Vero cells) (investigational vaccine) developed by Dalian Aleph Biomedical Co., Ltd. in healthy participants aged 10–60 years old is non-inferior to the lyophilized PVRV (positive control) manufactured by Liaoning Chengda Biotechnology Co., Ltd. (Shenyang, China), and that its safety is clinically acceptable. Method: A total of 2776 participants were enrolled in this study and divided into four groups: a five-dose test group, a five-dose control group, a four-dose test group, and a four-dose control group. The patients in the four-dose groups (Zagreb) were vaccinated on Days 0 (two doses), 7 (one dose), and 21 (one dose), and those in the five-dose groups (Essen) were vaccinated on Days 0, 3, 7, 14, and 28 (one dose each). The rabies-virus-neutralizing antibody assay with the RFFIT was used to assess the immunogenicity, and the adverse events (AEs) and serious adverse events (SAEs) were identified and collated. Results: The positive seroconversion rate was up to 100% on Days 14 and 35/42 after vaccination following any procedures in pre-immunization antibody-negative participants, and the positive seroconversion rate and geometric mean concentration (GMC) of the test groups (Zagreb and Essen vaccination procedures) was not inferior to that of the control groups. On Day 7 after vaccination, the immunogenicity of the Zagreb procedure with two doses of the vaccine on Day 0 was superior to the Essen procedure with one dose of vaccine, that is, the former had a higher seroconversion rate and RVNA titer. The non-inferiority criterion of immunogenicity was met for the whole population, the population aged 10–18 years and ≥18 years, and the pre-immunization antibody-positive population. The incidences of all AEs, solicited AEs, and unsolicited AEs in both groups were not statistically significant, and no vaccination-related SAEs were observed. Conclusion: The investigated vaccine is safe, its immunogenicity is non-inferior to that of the control vaccine, and the efficacy of the Zagreb procedure is superior to that of the Essen procedure 7 days after the first dose.

We evaluated the immunogenicity persistence of different immunization regimens of freeze-dried human rabies vaccine (Vero cells) in the 10–60 years age group of the Chinese population. Based on phase III clinical trials of Vero cells, participants who completed the full course of immunization were continuously enrolled in four-dose trial, five-dose, and five-dose control groups. Venous blood samples were collected 12 months after completion of the full immunization for rabies virus-neutralizing antibody (RVNA) testing, and the antibody-positive rate and geometric mean concentration (GMC) were calculated. Analysis of variance was used to compare three groups. The four-dose trial, five-dose trial, and five-dose control groups included 200, 186, and 214 participants, respectively. Twelve months after full immunization, the overall RVNA-positive rates were 97.00%, 93.55%, and 94.86% in the four-dose trial, five-dose control, and five-dose trial groups, respectively. The post-immunization RVNA GMCs values were 2.50, 2.05, and 2.04 IU/mL, respectively, with no statistically significant differences between them. Twelve months after full immunization, the overall RVNA-positive rate remained high, demonstrating satisfactory immunogenicity persistence for both immunization regimens.

Background: Host cell proteins (HCPs) from primary hamster kidney cells (PHKCs) used to produce rabies vaccines may cause an allergic reaction in humans, so these residual HCPs must be controlled. Establishing a national standard for PHKC HCP is very important to ensure the consistency of HCPs between batches of the vaccine and to standardize the control of HCPs. Objectives: We aimed to establish a novel national standard substance to determine the HCP residue in rabies vaccines produced with PHKCs. Methods: A two-step multi-laboratory collaborative collaboration was undertaken. In the first step, the protein concentration of the standard substance stock solution was determined using Lowry’s method. In the second step, the concentration of the candidate standard substance was determined with an enzyme-linked immunosorbent assay. Results: The concentration of the PHKC protein standard was 4.0 μg/mL (95% confidence interval: 3.5–4.4 μg/mL). Conclusions: The PHKC protein standard was approved by the Chinese National Committee on Standards for the quality control of PHKC-based rabies vaccines for human use, and it plays an important role in controlling the quality of these human vaccines.