Information has been received by the CDC concerning 16 patients at one daycare who were each vaccinated with one dose of varicella virus vaccine live. Subsequently, the patients experienced breakthrough varicella. In the building, there were 78 full time students with 74 of the children greater than 12 months of age. Of these 74 children, 58 had no history of chickenpox, and 16 had a history of chickenpox. Of the 58 children with no history of chickenpox, 42 had previously been vaccinated with varicella virus vaccine live, 1 was vaccinated with varicella virus vaccine live during the outbreak, and 15 had no vaccination with varicella vaccine live. Of the 42 vaccinated children, 16 developed breakthrough varicella. 14 of the cases were mild and defined as less than 50 lesions., and 2 cases were moderate and defined as 50-500 lesions. The remaining 16 vaccinated children did not experience a breakthrough rash. Of the 15 unvaccinated children, 8 developed natural varicella; 2 mild cases, 5 moderate cases and 1 severe case defined as greater than 500 lesions, and 7 had no rash (all of the 7 children were offered serologic testing of which 4 agreed, and they were all seronegative. Of the 74 children in the building, 46 attended preschool or pre-K continuously. Of the 46, 31 had no history of chickenpox, and 15 had a history of chickenpox. Of the 31 children with no history of chickenpox, 24 were vaccinated and 7 were not vaccinated. Of the 24 vaccinated, 12 developed breakthrough varicella and 12 did not have any rash. Of the seven unvaccinated children, six developed varicella and 1 was without rash. One patient in the group of students was the index case who developed a mild case of chickenpox following exposure to his sister who had herpes zoster. No further information is available. Per F/U 6/17/02: The 1st reported case had a rash onset date of 12/1/00 and the last reported date of rash onset was 1/11/01. No complications were reported during the outbreak. The median age of the case was 4 years (range 1-6), 76% were male. No cases occurred among infants less than 12 months of age (n-4) and none occurred in a child who had a prior history of varicella disease. One pt at the daycare developed herpes zoster during the outbreak (WAES 91072736). F/U info from a poster session titled "Low Varicella Vaccine Effectiveness in a Daycare Center Outbreak, New Hampshire. 12/00-2/01" was received. The report indicated that "95 (100%) parent and 94 (99%) provider questionnaires were returned. The median age of the 76 (80%) children who attended continously was 4.2 years (range: 6 months-8 years); 76% were male. Vaccination coverage was 76% of 23 cases of varicella, 15 (65%) occurred in vaccinated children and 8 (35%) occurred in unvaccinated children. The index case was a 4 year old vaccinee who developed BT on 12/1/00. The median age of cases was 4.4 years (range 1-7), VZV was cultured in 1 case and identified by PCR in another. Vaccine effectiveness was 40.5% (95% CI:-7.2; 67) overall and 41.7% in the building where the outbreak was centered.  Reported on 04/11/2003: "Follow-up information reported in a published article, title stated above that the vaccination coverage among children old enough to be eligible was 49 out of 67 children.  Lot numbers were verified for 46 out of 49 children.  The children were vaccinated during 1996 to 2000 with at least 33 different lots of vaccine administered by 28 different health care providers.  There was no evidence that any child had received expired vaccine.  There was a total of 25 cases of varicella with 17 cases having occurred in vaccinated children.  There were no cases in children with a history of varicella disease.  Of the 25 cases of varicella, 17 were mild and 8 were moderate or severe.  No child had a severe complication of varicella or required hospitalization.  As compared with unvaccinated children, whose who had been vaccinated had milder disease, had new lesions on fewer days, had rash that crusted more quickly, missed frewer days of day care, and were less likely to have fever.  In this outbreak, the effectiveness of varicella vaccine was 44 percent against diseases of any severity and 86 percent against moderate to severe disease.  An increased risk of vaccine failure was found among children who were vaccinated three or more years previous.  It was reported in an editorial that the varicella vaccine has proved to be exremely well tolerated with no serious safety issues emerging.  The "breakthrough" varicella may develop in 10 to 15 percent of the vaccinated population.  A copy of the published article is attached as further documentation of the patient's experience.