Venezuelan equine encephalomyelitis vaccine (strain TC-83): a field study.

In 1971, more than 370 horses in south Texas were studied with respect to their clinical, virologic, and neutralizing antibody responses to vaccination with Venezuelan equine encephalomyelitis (VEE) strain TC-83. This study confirms reported findings that the vaccine used in the 1971 epizootic in the lower Rio Grande Valley of Texas was safe and efficacious. Vaccinal virus viremia titers were generally below the postulated infection threshold of epizootic vectors. In general, reactions to the vaccine were minimal and transient, with no observed abortions or deaths attributable to use of the vaccine. Eleven months after vaccination, VEE antibody titers were demonstrable in most horses that had VEE antibodies within 30 days after vaccination. Presence of western equine encephalomyelitis antibody titers of greater than or equal to 1:50 at time of VEE vaccination appears to modify or to interfere with VEE antibody production.