This is a Phase 3, blinded, randomized study of SYN023 compared to a China licensed Human Rabies Immunoglobulin (a Rabies immune globulin from human sources, HRIG) for the prevention of rabies as part of post-exposure prophylaxis (PEP). The trial will enroll the World Health Organization (WHO) Category III rabies exposure subjects. The subject's death and rabies data will be reviewed by Data and safety monitoring board (DSMB) to confirm the safety. Besides, rabies vaccine would be administered after Study Drug in each group.

This trial is proposed to further the licensure of SYN023 to provide an effective PEP alternative available to those exposed persons who need such a product. A placebo-controlled rabies trial is unethical thus HRIG is selected as the control group. Rabies immune globulin from equine and human sources (HRIG) have been evaluated in many trials and HRIG is the standard of care in China.

This is a Phase 3, randomized, blinded, and active controlled study of SYN023 compared with a China licensed HRIG for PEP of patients who have been confirmed to have met all inclusion/exclusion criteria for their treatment group.

1000 patients aged 18 and above with the World Health Organization (WHO) Category III rabies exposure should be enrolled as planned and randomly assigned to the experimental group and the control group based on a ratio of 3: 1 through on-site stratification as part of PEP.

All subjects should receive wound infiltration injection of SYN023 or HRIG on Study Day 1 (wound conditions should be described and recorded before injection, including diameter, depth, expansion treatment, etc.), and should also simultaneously receive intramuscular injection of one dose of the freeze-dried rabies vaccine for human use (Vero cells) into the deltoid muscle. In accordance with the Essen Scheme, each subject also needs to receive one dose of the freeze-dried rabies vaccine for human use (Vero cells) on Study Days 4, 8, 15, and 29 respectively.

3.0 mL of venous blood samples should be collected 8 times from each subject prior to administration and on Study Day 4, 8, 15, 43, 99, 183, and 365 post administration of study drug. Relevant information should be collected from the subjects through follow-up visits, such as occurrence of rabies and survival conditions.

RVNA should be assayed through rapid fluorescence focus inhibition test (RFFIT).

Local adverse events related to the SYN023 injection sites and injection sites of the first dose and second dose of rabies vaccine, and systemic adverse events (AE) other than injection sites should be collected within 7 days after administration; local adverse events related to the injection sites of the third dose, fourth dose and fifth dose of rabies vaccine, and systemic adverse events (AE) other than the injection sites should be collected 7 days after administration. In addition, all adverse events occurring within 43 days after administration should be collected, and pregnancy conditions in 6 months after administration and all serious adverse events (SAE) occurring during the study period should be collected.

Inclusion Criteria:

1. Is age ≥18 years, on Study Day 1 with legal identification documents, and plan to live in the local administration area during the study;
2. Category III rabies exposure within 24 hours before Study Drug receipt ;
3. Completed written informed consent process, and signed the informed consent forms;
4. Subjects with the ability to understand the study procedure. And agreed to complete all follow-ups;
5. Female subjects are not in pregnancy (with negative results of urine pregnancy tests before vaccination) and are not in the period of breast feeding, and agree to avoid pregnancy within 121 days after administration;
6. Those who have an armpit temperature ≤ 37.0 °C.

Exclusion Criteria:

1. Previous receipt of equine or human (rabies) globulin or rabies vaccination prior to randomization;
2. Clinical evidence of rabies infection;
3. Category I and Category II rabies exposure;
4. Had fever (armpit temperature ≥ 38.5 °C) within 3 days before Study Day 1, or in the acute episode of any chronic diseases;
5. Received immunoglobulin or blood products (except for the anti-tetanus immunoglobulin) within 43 days before Study Day 1, or plan to use any such product (except for the anti-tetanus immunoglobulin) during the study;
6. Received systemic immunosuppressant medication such as systemic corticosteroids but not limited to systemic corticosteroids within 43 days before Study Day 1;
7. History of any immunodeficiency disease (for example: AIDS, systemic lupus erythematosus, etc.); or Laboratory evidence of previous or current immunodeficiency disease, including, but not limited to, any laboratory evidence of HIV infection;
8. History of spleen function deficiency or function injury, such as no spleen caused by any cause (such as splenectomy);
9. History of any severe allergy for vaccination, such as systemic urticaria, allergic laryngeal edema, anaphylactoid purpura, local allergic necrosis (Arthus reaction), angioedema, anaphylactic shock, etc., or allergic to any ingredient of the study drug/vaccine;
10. Previous receipt of any study product (drug, vaccine, biological product or medical device) within 6 months before Study Day 1, or plan to participate in any other clinical study during this study period;
11. History of or clinical evidence of any systemic disease, acute disease or chronic disease (such as convulsions, epilepsy, encephalopathy, nephrotic syndrome, etc.) that the investigator considers to be likely to interfere with safety or efficacy assessment of the study;
12. Previous medical history that may compromise the safety of the subject in the study according to the opinion of the principal investigator.

365 days

Blinding for drugs were carried out by the randomization statistician and other personnel who will not be involved in the implementation of the clinical trial. Under the guidance of the randomization statistician, blinding operators attach the printed labels with numbers to the outer packages of the study drug/control drug according to the blind codes and seal the packages with sealing stickers.

After the completion of blinding for drugs, the blind codes shall be sealed and kept by the randomization statistician. The entire blinding process must be documented. The personnel responsible for blinding must not participate in other relevant works during this clinical trial, and must not disclose the blind codes to any person participating in this clinical trial.