Clementina F. Geiser

ADMINISTRATION OF LIVE VARICELLA VACCINE TO CHILDREN WITH LEUKAEMIA

Live varicella vaccine was given to twenty-three children with lymphoreticular malignancies, twelve whose chemotherapy was complete and eleven who were still receiving therapy. Seroconversion was observed in all twenty-three children, only one of whom lost his vaccine-induced antibody. Eight of the children experienced thirteen exposures to varicella, including four continuing exposures in their households. Varicella, manifested by the appearance of seven vesicular lesions, developed in only one. In all but two of the children an invitro blastogenic response to varicella/zoster-virus (VZV) antigen developed; both children had a biphasic rash after immunisation. A sibling of one of these children seroconverted without clinical evidence of varicella, presumably because of infection with vaccine virus. None of the other household contacts had significant rises in VZV antibody. VZV was not isolated from the blood, throat, or urine samples of the twenty-three vaccinees tested.

946 A REASSESSMENT OF PASSIVE IMMUNIZATION AGAINST VARICELLA

Concern has been expressed about the efficacy of Varicella-Zoster Immune Globulin (VZIG) given intramuscularly (IM) to high risk individuals exposed to varicella. Perceived decreased efficacy may be due to more intensive chemotherapy and/or decreased potency of VZIG. Varicella-zoster antibody titers (VZAT) were determined by enzyme-linked immunosorbent assay for 21 normal adults and 23 susceptibles; the means and standard deviations were 0.600 ± 0.310, and 0.020 ± 0.0153 respectively. The seronegative range was defined as the mean for susceptibles +3 SD, ≤0.066. The peak mean VZAT in 7 seronegative VZIG recipients was 0.123 and, at 4-8 weeks, only 0.066. Thus, the peak VZAT provides minimal levels of antibody. Moreover, a second exposure following the usual incubation period would require an additional dose of VZIG. In contrast, 11 seronegative patients who received intravenous transfusions of platelets, white blood cells in plasma, or plasma alone had peak mean VZAT of 0.310. For 9/9 patients the duration of seropositivity lasted 4 weeks and for 2/5 as long as 12 weeks. Much higher peak titers of antibody were achieved than by IM VZIG (p 0.01 > 0.02) which might further reduce morbidity. Larger volumes of antibody could be given IV than IM, there is less pain, and thrombocytopenia would not be a deterent. Development of an IV VZIG preparation would appear to have a greater likelihood of reducing morbidity from varicella.

TOWARD THE ELIMINATION OF VARICELLA IN CHILDREN WITH LEUKEMIA

Varicella may produce significant illness in children with leukemia. To reduce morbidity, Varicella Vaccine (VV) was given as soon as possible following diagnosis of leukemia. Twenty-eight of 29 given VV no earlier than 1 year post diagnosis seroconverted; 1 developed mild varicella at 1 year and another at 2 years post immunization. In addition, 5 of 28 lost antibody. Only 10 of 17 children immunized earlier than 1 year post diagnosis had satisfactory responses to VV. Passive immunization was started at the time of diagnosis of leukemia to provide protection prior to the time active immunization could be successfully accomplished. VZIG produced low levels of antibody that was detectable <10-12 weeks. Patients who received transfusion of platelets, but not packed red blood cells, were found to have much higher antibody levels. Protection of children with leukemia can be achieved by giving VV one year post diagnosis. Prior to this time passive immunization, probably best accomplished with an intravenous product, could reduce morbidity from varicella in these high risk children.