VZIG prophylaxis in pregnant women is recommended to circumvent serious complications of chickenpox in adults. The objectives were 1) to establish the safety and efficacy of NP-001 VZIG (NP) in preventing or ameliorating maternal chickenpox infection 2) to compare the safety and efficacy of iv and im VZIG administration. Pregnant women who have no known immunity to chickenpox were enrolled. Patients were 1) stratified to either Group 1 or Group 2 (1-4 or 5-14 days post exposure, respectively) 2) randomly administered either im commercial VZIG (Control Group, CG), iv NP or im NP, and 3) followed-up 5 times within 6 weeks for physical exam and blood work (Biochemistry, CBC). VZV titers were done on baseline, 2 and 42 days post VZIG administration. Preliminary results indicate that 35% (10/28: 3 CG, 4 im NP, 3 iv NP) of Group 1 and 40% (6/15: 3 CG, l im NP, 2 iv NP) reported a relatively mild infection within 14 days of exposure. All laboratory results were not clinically significant. VZV titers have yet to be analyzed. No known major adverse event was noted. These preliminary results indicate that NP is safe and likely to be effective in preventing or lessening the effect of VZV infection whether it is given im or iv.