Persistence of immunity to varicella-zoster virus after vaccination of healthcare workers

ORJECTIVE: Varicella-zoster virus (VZV) vaccine is recommended to protect s usceptible healthcare workers (HCWs) from serious disease and to prevent no socomial spread of VZV. We evaluated clinical outcomes and serological resp onses in HCWs after immunization with live attenuated VZV vaccine. DESIGN: Vaccinees were immunized from 1979 to 1998 during VZV vaccine trial s, as well as after licensure, and followed prospectively for 1 month to 20 .6 (mean 4.6) years after vaccination. Sera were tested by fluorescent anti body to membrane antigen (FAMA), latex agglutination (LA), and enzyme-linke d immunoassay (EIA) to detect VZV-specific antibodies. STUDY PARTICIPANTS: The median age of the 120 HCWs was 26 years; 51 (42%) w ere males. INTERVENTIONS: Ninety eight (82%) of these study subjects received vaccine prepared by Merck and 22 (18%) by SmithKline Beecham; 25, 81, and 14 vaccin ees received one dose, two doses, and three doses, respectively. RESULTS: The crude attack rate was 10%; 12 of 120 HCWs developed chickenpox 6 months to 8.4 years after vaccination. The attack rates following househ old and hospital exposures were 18% (4/22) and 8% (6/72), respectively. All resulting illness was mild to moderate (mean 40 vesicles). Seroconversion after vaccination was documented by FAMA in 96% of HCWs, although 31% lost detectable antibodies. Compared with FAMA, LA and EIA were 82% and 74% sens itive and 94% and 89% specific, respectively. CONCLUSIONS: The VZV vaccine effectively protected HCWs from varicella, par ticularly from serious disease. Currently available serological tests are n ot optimal, and improved assays are needed (Infect Control Hosp Epidemiol 2 001;22:274-283).