Bioterrorism remains as one of the biggest challenges to global security and public health. Since the deadly
anthrax attacks of 2001 in the United States, Bacillus anthracis and Yersinia pestis, the causative agents of
anthrax and
plague, respectively, gained notoriety and were listed by the CDC as Tier-1 biothreat agents. Currently, there is no Food and Drug Administration-approved
vaccine against either of these threats for mass vaccination to protect general public, let alone a
bivalent vaccine. Here, we report the development of a single
recombinant vaccine, a triple
antigen consisting of all three target
antigens, F1 and V from Y. pestis and PA from B. anthracis, in a structurally stable context. Properly folded and soluble, the triple
antigen retained the functional and immunogenicity properties of all three
antigens. Remarkably, two doses of this immunogen adjuvanted with Alhydrogel® elicited robust antibody responses in mice, rats, and rabbits and conferred complete protection against inhalational
anthrax and
pneumonic plague. No significant antigenic interference was observed. Furthermore, we report, for the first time, complete protection of animals against simultaneous challenge with Y. pestis and the lethal toxin of B. anthracis, demonstrating that a single biodefense
vaccine can protect against a bioterror attack with weaponized B. anthracis and/or Y. pestis. This bivalent
anthrax-
plague vaccine is, therefore, a strong candidate for stockpiling, after demonstration of its safety and immunogenicity in human clinical trials, as part of national preparedness against two of the deadliest bioterror threats.