Persistence of Human Antibody to Venezuelan Equine Encephalomyelitis (VEE) Virus Subtypes after Immunization with Attenuated (TC-83) VEE Vaccine.

The persistence of serum antibody of Venezuelan equine encephalomyelitis VEE virus subtypes was studied in 20 volunteers inoculated 7 or 9 years previously with attenuated TC-83 VEE vaccine. Serological patterns were compared with those of 10 other persons bled 28 days after vaccination with TC-83. Vaccinees had no other known group A arbovirus exposure. Neutralizing antibody titers of 110 were measured against the homologous TC-83 virus strain in all long- and short-term vaccinees. In both groups of vaccinees the percentage of antibody-positive persons and their geometric mean titers were higher against the epizootic subtypes I-A, I-B, I-C, than against the enzootic subtypes, I-D, I-E, II, III, and IV. However proportionally fewer long-term vaccinees than short-term vaccinees, had detectable neutralizing antibody reactive with enzootic strains. These results reveal long-lasting circulation of neutralizing antibody to TC-83 virus and closely related epizootic variants in 95-100 of vaccinees. The relatively lower antibody conversion rate and loss of antibody to more antigenically remote enzootic VEE subtypes suggests that vaccinees may be less well protected against infection by these strains.