Safety, Reactogenicity, and Immunogenicity of a Recombinant Protective Antigen Anthrax Vaccine Given to Healthy Adults

Abstract

BACKGROUND: Bacillus anthracis causes anthrax, a vaccine-preventable zoonotic disease that may follow intentional or unintentional exposure to its spores. Although an anthrax vaccine is currently licensed in the USA, better vaccines are desirable for both pre- and post-exposure prophylaxis.METHODS: Healthy adults, aged 18 to 40 years, received anthrax immunization with either licensed Anthrax Vaccine Adsorbed (AVA, BioThrax™), or an experimental recombinant Protective Antigen vaccine (rPA) produced from an avirulent, non-spore-forming strain of B. anthracis at one of 4 doses (5, 25, 50, or 75 μg). Volunteers were followed for safety, reactogenicity, and immunogenicity.RESULTS: rPA vaccine was well tolerated with a low rate of local or systemic reactions. Although antibody responses were poor following unadjuvanted rPA administration, 89 and 100% of volunteers who received Alhydrogel-adjuvanted rPA given intramuscularly had 4-fold increases by enzyme-linked immunosorbent and toxin neutralization assays, respectively. Peak antibody responses to adjuvanted rPA given intramuscularly were equivalent to AVA, given either intramuscularly or subcutaneously, when measured by either assay.CONCLUSION: This recombinant Protective Antigen anthrax vaccine, when given with the adjuvant Alhydrogel to healthy adults in 2 intramuscular injections 4 weeks apart, is very well-tolerated and highly immunogenic.