Kinetics of formation of neutralizing antibodies against vaccinia virus following re-vaccination

Administration of vaccinia immune globulin (VIG), derived from vaccinated healthy adult volunteers, is the treatment-of-choice for patients suffering from severe complications following smallpox vaccination. The present study was aimed to determine the time interval after vaccination, at which the highest titer of neutralizing antibodies is obtained. Ninety-nine 18-year-old soldiers, immunized with vaccinia virus at birth, participated in the study, 87 of whom had detectable antibodies against vaccinia virus prior to re-vaccination. Their initial average neutralizing antibodies titer (NT₅₀) was 27. Fourteen days after re-vaccination the titer reached 152 and then dropped to 136, 119, 110 and 87 at 21, 30, 45 and 60 d, respectively. The titers of vaccinia antibodies induced in vaccinees without detectable antibodies at the start of the study, were significantly lower and the titers observed after re-vaccination were: 62, 56, 66, 38 and 34, at 14, 21, 30, 45 and 60 d, respectively. In an additional study, 65 volunteers vaccinated at birth and again at the age of 8 years old were re-vaccinated. Fourteen days later their NT₅₀ was higher than those vaccinated only at birth. It can be concluded that bleeding of vaccinees 14 d following re-vaccination is the preferable time for the preparation of VIG.