Vaccine Info

RiVax Ricin Toxin Vaccine

Authored by
Last reviewed
December 12, 2021
Fact checked by
Robert Carlson, MD

RiVax Ricin Toxin Vaccine Description

RiVax Ricin Toxin Vaccine is Soligenix's proprietary heat stable recombinant subunit vaccine developed to protect against exposure to ricin toxin. RiVax® contains a genetically altered version of a Ricin Toxin A (RTA) chain containing two mutations that inactivate the ricin molecule's toxicity, invented initially at the University of Texas Southwestern

RiVax uses Soligenix's proprietary ThermoVax® technology that creates a thermostabilized vaccine candidate that can be stored at room temperature for extended periods, making it compatible with United States government stockpiling requirements.

The thermostabilized version of RiVax is produced by lyophilizing (freeze-drying) the vaccine in individual vials to form a solid white cake. This removes water and other components from the material, which would otherwise destabilize the protein. Instead, by using a proprietary process, the protein-aluminum combination remains intact.

The solid, lyophilized material can then be returned to a liquid form immediately before use by simply adding sterile water and mixing before injection. Because sterile water is also very common and very stable, this results in an extremely convenient product that can be stored for extended periods. Long-term storage and ease of use are key attributes for a product that may be stockpiled.

The RiVax vaccine candidate uses a modified inactivated protein component of the ricin toxin to raise antibody responses, combined with an alum adjuvant to boost the body’s response to the vaccine. RiVax induces human adaptive immune systems to produce antibodies that recognize and bind ricin toxin, preventing it from getting inside cells and killing them. After intramuscular injection with RiVax, IgG and other antibodies are produced and circulate within the body and can mop up ricin whether inhaled, eaten, or injected.

RiVax primarily consists of two components: A modified form of the A-chain of the ricin toxin. The modifications have removed the biological activity of the protein while still retaining its shape to trigger an effective antibody response; Aluminum (“alum”) as an adjuvant. Alum is a very well-known adjuvant used in many commercial vaccines, with well-known safety profiles.

Approval for RiVax is being pursued under the U.S. FDA "Animal Rule," which is applied to products where testing in clinical efficacy trials would be unethical. For example, in the case of a ricin toxin vaccine, clinical efficacy testing is unethical since it would require intentionally exposing humans to ricin toxin.

RiVax® has received Orphan Drug and Fast Track designations from the FDA and, upon approval, has the potential to qualify for a biodefense Priority Review Voucher. In addition, RiVax® has received Orphan Drug designation from the European Medicines Agency.

Soligenix, Inc. is a late-stage biopharmaceutical company (Nasdaq: SNGX) focused on developing and commercializing products to treat rare diseases where there is an unmet medical need.

RiVax Ricin Toxin Vaccine Indication

RiVax Ricin Toxin Vaccine candidate is indicated to prevent death following exposure to a lethal dose of ricin toxin. Ricin toxin is a deadly yet easily manufactured white powder that can induce irreversible symptoms within four hours of exposure and may cause death within 48-72 hours. 

Ricin toxin causes cell death once it penetrates the cell membrane. Ricin toxin can penetrate cells within 4 hours of exposure. Depending on the route of exposure (ingestion, inhalation, or injection), ricin toxin has different initial symptoms. Regardless of the initial route of exposure, ricin poisoning results in death with sufficient exposure.

RiVax Ricin Toxin Vaccine Dosage

RiVax is administered as an intramuscular injection on 2 or 3 occasions, resulting in the adaptive immune system mounting an antibody response.

RiVax induces the adaptive immune system to produce antibodies that recognize and bind ricin toxin, preventing it from getting inside cells and killing them. After intramuscular injection with RiVax®, IgG and other antibodies are produced and circulate within the body and can mop up ricin whether it was inhaled, eaten, or injected.

RiVax Ricin Toxin Vaccine News

November 4, 2021 - Soligenix, Inc. announced the publication of pre-clinical immunogenicity studies for RiVax® demonstrating enduring protection for at least 12 months post-vaccination. The article "Durable Immunity to Ricin Toxin Elicited by a Thermostable, Lyophilized Subunit Vaccine" has been accepted for publication in the journal mSphere. The article results from collaborative work with the Wadsworth Center of the New York State Department of Health. Coupled with the previous demonstration of efficacy in mice and non-human primates (NHPs) as well as long-term thermostability (at least one year at 40°C or 104°F), these results reinforce the practicality of stockpiling and potentially utilizing the RiVax vaccine in warfighters and civilian first responders without the complexities that arise for vaccines that require stringent cold chain handling.

December 8, 2020 - RiVax Ricin Toxin Vaccine is pursuing approval under the U.S. FDA "Animal Rule," applied to products where testing in clinical efficacy trials would be unethical. In the case of a ricin toxin vaccine, the vaccine's testing would be unethical since it would require exposing humans to ricin toxin. According to the CDC, Ricin is a poison found naturally in castor beans. Ricin can be found in many forms, including powder, mist, pellet, and can also be dissolved in water.  It is considered a weapon of terror based upon its stability and high potency and the fact that it is readily extracted from by-products of castor oil production.

RiVax Ricin Toxin Vaccine Clinical Trials

RiVax® studies have been supported by a contract (#HHSN272201400039C) award of approximately $21.2 million from the National Institute of Allergy and Infectious Diseases (NIAID). In addition, non-dilutive funding for the development of RiVax® has exceeded $40 million to date.

NCBI Phase 1: A pilot clinical trial of a recombinant ricin vaccine in normal humans.

NCBI Phase 1B:  Pilot Phase IB Clinical Trial of an Alhydrogel-Adsorbed Recombinant Ricin Vaccine. Clinical Trial NCT00812071: Phase 1B Study of RiVax, a Vaccine to Prevent the Toxic Effects of Ricin (FDA-OPD)

These studies suggest that RiVax/alum is safe and induces higher titers of total and neutralizing antibodies.