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

The research article details a study conducted in 1971 on over 370 horses in South Texas, examining their responses to a Venezuelan equine encephalomyelitis (VEE) vaccine. The results confirmed previous findings that the vaccine was safe and effective, resulting in minimal and transient reactions with no attributable abortions or deaths.

Study Design and Execution

• The research was a field study carried out in 1971, focusing on more than 370 horses in south Texas.
• The study aimed to observe the horses’ clinical, virologic, and neutralizing antibody responses to the Venezuelan equine encephalomyelitis (VEE) vaccine, utilising strain TC-83.
• The study served to confirm findings previously reported regarding the safety and efficacy of the vaccine.

Key Findings

• In general, the horses’ viremia titers (a measurement of the amount of virus in the bloodstream) after vaccination were below the postulated infection threshold of epizootic vectors, essentially below a level likely to cause an outbreak of disease in these horses.
• The horses’ reactions to the VEE vaccine were minimal and transient, indicating that the vaccine was generally well tolerated.
• Notably, there were no observed abortions or deaths attributable to the use of the vaccine in the study sample.
• Most horses that had VEE antibodies within the first 30 days after vaccination still showed these antibodies eleven months after vaccination, indicating a long-term immune response to the vaccine.

Additional Findings

• The presence of western equine encephalomyelitis antibody titers in horses, of an amount greater than or equal to 1:50 at the time of VEE vaccination, seemed to interfere with or modify VEE antibody production. This suggests that prior immunity to other diseases may impact the efficacy of the VEE vaccine but more research is needed on this topic.