Effectiveness of oral aciclovir in preventing maternal chickenpox: A comparison with VZIG

Objectives: Although often presenting as a self-limiting childhood disease, chickenpox can have serious consequences if acquired in pregnancy. Until April 2022, the UK recommendations were that varicella immunoglobulin (VZIG) should be administered intramuscularly to susceptible pregnant women exposed to chickenpox prior to 20 weeks gestation. Oral aciclovir or VZIG was recommended if exposure occurred at 20+ weeks gestation. Our objective was to compare the effectiveness of oral aciclovir to VZIG in preventing maternal and neonatal chickenpox. Methods: We identified and followed up 186 pregnant women who were exposed to chickenpox and compared their outcomes. Results: 171/186 (91.9%) of these women received either VZIG or oral aciclovir. Of the 145 women who received VZIG, 53/145 (36.6%) went on to develop chickenpox compared to 8 of the 26 (30.8%) women who received oral aciclovir (p = 0.32). No statistical difference was found between the oral aciclovir and VZIG groups even after controlling for maternal age, gestational stage, type of exposure and IgG titre (adjusted OR:0.83; 95%CI:0.26–2.65; p = 0.75). Conclusions: These findings support the use of oral aciclovir as first-line prophylaxis in pregnant women exposed to varicella as they suggest its effectiveness at preventing maternal chickenpox is either better or equal to VZIG.