Comparison of two strategies to prevent varicella outbreaks in housing facilities for asylum seekers

Background: The proportion of adults with positive varicella serology is lower in populations from tropical countries. Therefore immigrants to countries with a temperate climate are at risk of acquiring varicella infection during adulthood. Methods: We tested two different strategies to prevent varicella outbreaks in housing facilities for asylum seekers arriving in the Canton of Vaud, Switzerland. The first strategy consisted of a rapid response with isolation of the affected individuals and vaccination of the susceptible contacts. The second strategy consisted of a general vaccination upon arrival of all asylum seekers aged 15-39 years with no history of chickenpox. Results: From May 2008 to January 2009 we applied the rapid response strategy. Eight hundred and fifty-eight asylum seekers arrived in the Canton and an attack rate of 2.8% (seven cases among 248 exposed asylum seekers) was observed. The mean cost was US$ 31.35 per asylum seeker. The general vaccination strategy was applied from February 2009 to May 2010, a period during which 966 asylum seekers were registered. This second strategy completely prevented any outbreak at a mean cost of US$ 83.85 per asylum seeker. Conclusions: Of the two analyzed interventions to prevent varicella outbreaks in housing facilities for asylum seekers, the general vaccination strategy was more effective, more sustainable, and ethically preferable, although more costly. (C) 2011 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.