Several of the vaccine recipients experienced fevers classified

as grade 3, based on the current adverse event grading scale. Viral shedding that occurred in a subset of the recipients appeared to coincide with sore throat and/or fevers. Based on these findings, clinical testing of V3526 was discontinued. Since a high frequency of adverse reactions has been associated with live-attenuated VEEV vaccines [9], [10] and [16], licensure of a live-attenuated vaccine will likely be faced with significant regulatory obstacles relating to safety. Our strategy to develop a VEEV vaccine was revised to focus on a non-infectious virus vaccine. The use of C84 was not considered for further Selleckchem Navitoclax development because the Department of Defense, in 1996, deemed this vaccine in need of improvement. C84 was last selleckchem manufactured between 1980 and 1981 and the limited supply of C84 vaccine has been in storage for over

29 years and the recent potency and stability of this vaccine are unknown. Manufacture of new lots of C84 is unlikely to occur because this would require re-derivation of the TC-83 stock, followed by GMP production of the TC-83 in a certifiable cell line and further development of the entire TC-83/C84 manufacturing process. In addition, a technical review of the C84 manufacturing records failed to identify a credible source document describing the actual manufacturing process and testing scheme therefore this would also need to be devised. Having a large inventory of GMP manufactured V3526 originally

reserved for the clinical testing, the decision was made to inactivate V3526 for the production of VEEV vaccine candidates that would ultimately replace C84 and be used as a primary vaccine to protect personnel at risk to accidental or intentional VEEV exposure. Studies were initiated using formalin to inactivate V3526 with the intent of producing a vaccine with a significantly reduced adverse reaction profile compared to second V3526, but one that retains potential as a protective immunogen against VEEV infection and performs similarly or better than C84. Formalin inactivation of virus has been successfully used to develop safe and efficacious human and veterinary vaccines since 1955 [17] and most recently, an inactivated vaccine for Japanese encephalitis virus [18]. The use of formalin inactivation for virus vaccine development is attractive from a safety perspective in that the virus cannot revert to virulence, since there is no virus replication during immunization. The use of formalin to inactivate viruses is also attractive from a manufacturing perspective as the inactivation process is relatively simple to develop. In the development of a formalin inactivated VEEV vaccine candidate, we recently developed a method to inactivate V3526 using formalin and established a system of prioritized assays to evaluate residual infectivity and preservation of immunologically essential epitopes [19].