VaxGen’s rPA102 Recombinant Anthrax Vaccine

On April 15, 2004 VaxGen, Inc. announced that it had started the Phase II clinical testing of rPA102, its recombinant anthrax vaccine. VaxGen indicated that this 13-month trial is one of two studies under a $80.3 million agreement with the NIH’s National Institute of Allergy and Infectious diseases. The purpose of this study, involving 480 healthy volunteers, is to determine the immunogenicity and safety of various rPA102 formulations. The vaccine contains both rPA (recombinant Protective Antigen) and an adjuvant (aluminum hydroxide), which increases or enhances the immune response. In March 2004, at the International Conference on Emerging Infectious Diseases, VaxGen reported that a Phase I trial of rPA102 demonstrated that the vaccine produced an immune response comparable to that of Anthrax Vaccine Adsorbed (AVA). This study reportedly showed that rPA102 was well tolerated, with no significant safety or reactogenicity issues.

rPA is a recombinant, synthetic protein that is postulated to prevent the complications of anthrax infection by inducing antibodies that bind to and neutralize potent anthrax toxins. The only currently available vaccine for anthrax in the United States is AVA, which requires a primary series of three subcutaneous injections given 2 weeks apart, followed by three additional subcutaneous injections given at 6, 12, and 18 months. Annual booster injections of the vaccine are recommended thereafter.

In December 1997, the U.S. Department of Defense announced a plan to vaccinate all U.S. military personnel with AVA. As of April 2000, 425,976 service members had received 1,620,793 doses of anthrax vaccine under the DoD’s Anthrax Vaccine Immunization Program. In October/November 2001, approximately 10,000 persons were advised to take 60 days of post exposure prophylaxis because of potential exposure to anthrax in several U.S. states as a result of a bioterror attack. 22 cases of anthrax resulted from this intentional release of Bacillus anthracis.

While data released by VaxGen for rPA102 looks promising, it is very preliminary in nature. Ideally, the next anthrax vaccine would have an improved safety and efficacy profile when compared to AVA as well as the benefit of a simplified dosing schedule. As for the degree of impact of an anthrax vaccine, the ongoing assessments by the U.S. government and its Advisory Committee on Immunization Practice concerning the potential risk of an anthrax outbreak are critical. Currently, Biohorizon maintains its Moderate Impact Technology designation for rPA102 and recommends no specific assessment activities for this vaccine.

Technology Details
Target Disease / Indication: Anthrax
Technology Classification: Drug/Vaccine
Body System: Multiple Systems
Program Area: Medicine/Infectious Disease
Regulatory Status: Phase II
BioHorizon Impact Score: 48/100 – Moderate