Use of telemetry to assess vaccine-induced protection against parenteral and aerosol infections of Venezuelan equine encephalitis virus in non-human primates.

Two investigational vaccines, TC-83 (live-attenuated) and C-84 (formalin-inactivated), are currently available to immunize at-risk individuals against Venezuelan equine encephalitis virus (VEE). Ideally, such vaccines should protect against both the natural mosquito-borne route of infection and from aerosol, the most common route of laboratory infection. Whereas considerable data on vaccine efficacy following parenteral challenge are available, the efficacy of these vaccines against disease caused by aerosol exposure is not well established in primates. We compared the immunogenicity and protective capacity of TC-83 and C-84 against either subcutaneous or aerosol routes of infection in cynomolgus monkeys implanted with temperature-monitoring radiotelemetry devices. A single s.c. dose of TC-83, or three s.c. doses (days 0, 7, 28) of C-84, elicited similar serum virus-neutralizing antibody responses. Animals immunized with either TC-83 or C-84 were protected against s.c. infection. In contrast, after aerosol infection, 40% of the animals vaccinated with either TC-83 or C-84 developed signs nearly as severe as those seen in unvaccinated animals. Protection was not entirely consistent with the measured preinfection immune responses: unprotected animals had serum virus-neutralizing antibody titers and lymphoproliferative responses similar to those seen in protected animals. In this study, C-84 (three doses) protected monkeys as well as TC-83 (one dose) against either a s.c. or aerosol VEE challenge.