THE EFFECT OF DECREASING AMOUNTS OF LIVE VIRUS, WHILE ANTIGEN CONTENTREMAINS CONSTANT, ON IMMUNOGENICITY OF OKA MERCK VARICELLA VACCINE

The purpose of the study was to establish the minimum immunizing dose of stored Oka/Merck varicella vaccine and mimic effects of prolonged s torage of vaccine at freezer temperatures. Ninety children were random ized to one of three groups: group A (1770 pfu/dose), group B (400-500 pfu/dose), or group C (80-160 pfu/dose). Seroconversion rates for gro ups A-C were 97%, 96%, and 92%, respectively. Group A and B vaccinees had higher antibody titers at 1 year than did group C subjects (P = .0 1). The difference between groups B and C approached significance (P = .058). At 1 year after immunization, 73%,83%, and 80% in groups A-C, respectively, demonstrated cell-mediated responses. Since freshly reco nstituted vaccine contains 1770 pfu/dose, vaccine failure from loss of potency is unlikely if vaccine is stored properly and administered pr omptly after reconstitution.