Introduction. Casa Garrahan (CG) accommodates children with complex conditions referred nationwide; these children are seen in children's hospitals located in the Autonomous City of Buenos Aires. Varicella is a highly-contagious disease, with attack rates of up to 90% among susceptible individuals. In closed communities, the implementation of outbreak control measures is critical. Objectives. To describe the characteristics of children exposed to varicella at CG, the implemented prophylaxis measures and their effectiveness. Methods. Prospective, cohort study. Children exposed to varicella at CG between2008 and 2013, their demographic and clinical characteristics, immunization and/or history of varicella, prophylaxis measures, and secondary attack rate were assessed. Results.

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107. Fifty-three percent (n: 57) were girls. Their median age was 84 months old [interquartile range (IQR): 24-144]. Ninety-five percent (n: 102) had an underlying disease [hemato-oncological disease: 39% (n: 42); neurological disease: 18% (n: 19); congenital heart disease: 9% (n: 10); and post-operative period: 65 (n: 6)]. Fifty percent had some degree of immunosuppression (n: 54). Twenty-nine percent (n: 31) referred to have had varicella; 27% (n: 29) indicated that they never had the infection; and 41% (n: 44) did not recall a history of varicella. Only 3% (n: 3) had been vaccinated. Based on their immune status, age and history of varicella, acyclovir was indicated as prophylaxis in 61% (n: 65); immunization in 10% (n: 10); and gamma globulin in 1 patient. No adverse effects were observed in relation to the different prophylaxis measures. No secondary cases were observed at 30 days. Conclusions. Implemented measures were effective to prevent secondary cases. Among healthy and immunocompromised children, prophylaxis with acyclovir was effective and well-tolerated.