- Primary varicella (PV) presents a public health risk for adults in closed residential settings, especially for immigrants from tropical areas where infection during childhood is less likely. In this study, an outbreak of PV at a detention facility for illegal immigrants from Eritrea and Sudan in southern Israel is described. Basic demographic information and clinical course for all cases were obtained. One hundred and nine cases of PV, all in young adult men aged 18-40 years, were diagnosed over a 7-month period (June to December 2012). Diagnosed patients were placed in quarantine until the resolution of illness without other public health measures being implemented. The Israeli Ministry of Health was notified of the outbreak in early December and recommended two doses of varicella vaccine for all susceptible detainees and staff. Within 2 weeks of completion of the first dose of vaccine, there was only one additional case in a detainee immunized 13 days prior to diagnosis. The effectiveness of vaccination in halting the outbreak was immediate, despite the fact that 15.6% of detainees refused to be immunized. The possible roles of vaccination or natural infection in achieving herd immunity and thereby ending the outbreak in this population are discussed. We recommend considering early vaccination for all when an outbreak or a series of connected cases is detected in a closed-residential setting such as the detention facility described here.