4. MEASURES IN MATERNAL VARICELLA-ZOSTER VIRUS INFECTIONS 4.1. Preventive Measures An effective prophylaxis of chickenpox in pregnant women and neonates is only possible by active immuni-zation of seronegative women before pregnancy. A live attenuated varicella vaccine has been shown to be safe and effective in preventing chickenpox in adults [39]. Varicella vaccine, as all live-attenuated vaccines, is con-traindicated in pregnant women and pregnancy has to be avoided for at least 4 weeks following vaccination. The Pregnancy Registry managed by the Merck Research Laboratories (USA) in collaboration with the Centers for Disease Control and Prevention (USA), records women, who exposed to varicella vaccine during pregnancy or within 3 months before conception. Preliminary results showed no hints to any birth defects related to vaccine exposure [40,41]. In few cases, vaccines can develop breakthrough varicella that occurs 42 days after vaccina-tion and represents wild virus infection [42]. Most dis-eases are very mild, the infectivity is relatively low and there is a low or no risk for complications [43]. Thus, the risk for CVS from breakthrough varicella can be regarded as considerably lower than that for CVS in unvaccinated women with varicella. However, prophylactic and thera-peutic measures in women with breakthrough varicella should be considered as in unvaccinated women who develop varicella since data about the risk for CVS after breakthrough varicella are not available to date. Non-immune pregnant women should be advised to avoid exposure to chickenpox and zoster. If pregnant