Soligenix has reported positive results from a Phase Ib clinical trial of RiVax recombinant subunit vaccine, developed to protect against exposure to ricin.

The Aluminum hydroxide adjuvanted RiVax was found to be safe and well tolerated in the study and induced better ricin neutralising antibody levels in humans compared to adjuvant-free RiVax.

Soligenix chief scientific officer Dr Robert Brey said the positive results meant the company could now develop the vaccine further and initiate more definitive human trials.

"The Phase Ib results demonstrate that well characterised adjuvants can improve the performance of highly purified subunit antigens such as the one contained in RiVax," Brey said.

"The next steps for the development of RiVax will include the evaluation of secondary adjuvants to enhance the induction of neutralizing antibodies in fewer doses and the employment of our ThermoVax technology to stabilize the ingredients of the vaccine for long term storage at ambient temperature conditions."

The trial was conducted in healthy volunteers to evaluate the long-term safety and immunogenicity of escalating doses of the vaccine up to one year, after a primary vaccination.

The study reported that the vaccine was well tolerated with mild side effects that are characteristic of reactions to intramuscularly injected vaccines, and all of the subjects developed neutralising antibodies against ricin toxin at peak antibody titers, determined two weeks after the third vaccination.

All of the subjects who received either the high dose (100 micrograms) or low dose (10 micrograms) vaccine in the Phase Ib trial were 100% seropositive at nine months after the first vaccination, with 60% remaining positive at one year.