Persistence in humans of antibody after immunization with four alphavirus vaccines.

Immunization with attenuated VEE virus vaccine resulted in persistence of neutralizing antibody for 12 years. Immunization with inactivated WEE vaccine converted 83% of the subjects, killed EEE vaccine converted 27% and killed Chikungunya vaccine induced no significant titers. Antibody formed as a result of immunization with inactivated vaccines was of short duration, i.e. less than 1 year. Attenuated VEE was responsible for some heterologous antibody rises to the other three alphaviruses. Among the inactivated vaccines WEE and Chikungunya vaccines produced one heterologous rise each to EEE virus.