Vaccine Info

RiVax Ricin Toxin Vaccine

Authored by
Last reviewed
February 15, 2023
Fact checked by
Robert Carlson, MD

RiVax Ricin Toxin Vaccine Description

Soligenix, Inc. RiVax® vaccine is a proprietary heat-stable recombinant subunit vaccine developed to protect people 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 primarily consists of two components: 1.) 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; 2.) Aluminum ("alum") as an adjuvant. 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, circulate within the body, and can mop up ricin whether inhaled, eaten, or injected.

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 U.S. 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 adding sterile water and mixing before injection. Because sterile water is also widespread 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.

Approval for RiVax is being developed under the U.S. Food and Drug Administration (FDA) "Animal Rule," which is applied to products where testing in clinical efficacy trials would be unethical. RiVax received Orphan Drug and Fast Track designations from the FDA. In addition, RiVax has received an Orphan Drug designation from the European Medicines Agency. As a new chemical entity, an FDA-approved RiVax vaccine has the potential to qualify for a biodefense PRV, which allows the holder an accelerated review of a drug application. 

On December 20, 2022, the Company announced RiVax®-Vaccinated NHP survival was statistically significantly correlated with an epitope-specific serum assay (EPICC) prior to challenge. The journal npj Vaccines published a related study on December 16, 2022.

The development of RiVax® has been funded through a series of grants from both the National Institute of Allergy and Infectious Diseases (NIAID) and the U.S. FDA, and ongoing development is sponsored by NIAID contract #HHSN272201400039C. 

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 Indication

RiVax Ricin Toxin Vaccine is indicated to prevent death following exposure to a lethal dose of ricin toxin that causes cell death once it penetrates the cell membrane. Ricin toxin can penetrate cells within four 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.

The Company says the successful development of an effective vaccine against ricin toxin may act as a deterrent against the actual use of ricin as a biological weapon and could be used to vaccinate military personnel and civilian emergency responders at high risk of potential exposure in the event of a biological attack. There are no FDA-approved prophylactic or post-exposure therapies for ricin toxin exposure.

RiVax Dosage

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

December 20, 2022 - Soligenix, Inc. announced today the publication of preclinical immunogenicity challenge studies for RiVax® demonstrating statistically significant correlates of protection predicting survival after lethal aerosolized ricin challenge in non-human primates.

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.

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.

RiVax 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). 

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.