title: Impact of the US Two-dose Varicella Vaccination Program on the Epidemiology of Varicella Outbreaks: Data from Nine States, 2005-2012.
abstract: BACKGROUND
  A routine 2-dose varicella vaccination program was adopted in 2007 in the US to help further decrease varicella disease and prevent varicella outbreaks. We describe trends and characteristics of varicella outbreaks reported to the Centers for Disease Control and Prevention (CDC) during 2005-2012 from 9 states.
  
  
  METHODS
  Data on varicella outbreaks collected by 9 state health departments were submitted to CDC using the CDC outbreak reporting worksheet. Information was collected on dates of the outbreak, outbreak setting and number of cases by outbreak; aggregate data were provided on the numbers of outbreak-related cases by age group, vaccination status and laboratory confirmation.
  
  
  RESULTS
  Nine hundred and twenty-nine outbreaks were reported from the 6 states, which provided data for each year during 2005-2012. Based on data from these 6 states, the number of outbreaks declined by 78%, decreasing from 147 in 2005 to 33 outbreaks in 2012 (P = 0.0001). There were a total of 1015 varicella outbreaks involving 13,595 cases reported by the 9 states from 2005 to 2012. The size and duration of outbreaks declined significantly over time (P < 0.001). The median size of outbreaks was 12, 9 and 7 cases and median duration of outbreaks was 38, 35 and 26 days during 2005-2006, 2007-2009 and 2010-2012, respectively. Majority of outbreaks (95%) were reported from schools, declining from 97% in 2005-2006 to 89% in 2010-2012. Sixty-five percent of outbreak-related cases occurred among 5-year to 9-year olds, with the proportion declining from 76% in 2005-2006 to 45% during 2010-2012.
  
  
  CONCLUSIONS
  The routine 2-dose varicella vaccination program appears to have significantly reduced the number, size and duration of varicella outbreaks in the US.
authors.affiliation: From the *Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia; †Division of Immunization, Michigan Department of Community Health, Lansing, Michigan; ‡Vermont Department of Health, Burlington, Vermont; §Immunization Branch, California Department of Public Health, Richmond, California; ¶Vaccine-Preventable Disease Unit, Minnesota Department of Health, St. Paul, Minnesota; ‖Office of Epidemiology, Mississippi State Department of Health, Jackson, Mississippi; **West Virginia Department of Health and Human Resources, Charleston, West Virginia; ††Infectious Disease Epidemiology and Outbreak Response Bureau, Center for Immunization, Maryland Department of Health and Mental Hygiene, Baltimore, Maryland; ‡‡Disease Control and Environmental Epidemiology Division, Colorado Department of Public Health and Environment, Denver, Colorado; and §§Infectious Disease Control Unit, Texas Department of State Health Services, Austin, Texas.
authors.forename: Jessica
authors.initials: J
authors.lastname: Leung
authors.forename: Adriana S
authors.initials: AS
authors.lastname: Lopez
authors.forename: Joel
authors.initials: J
authors.lastname: Blostein
authors.forename: Nancy
authors.initials: N
authors.lastname: Thayer
authors.forename: Jennifer
authors.initials: J
authors.lastname: Zipprich
authors.forename: Anna
authors.initials: A
authors.lastname: Clayton
authors.forename: Vicki
authors.initials: V
authors.lastname: Buttery
authors.forename: Jannifer
authors.initials: J
authors.lastname: Andersen
authors.forename: Carrie A
authors.initials: CA
authors.lastname: Thomas
authors.forename: Maria
authors.initials: M
authors.lastname: Del Rosario
authors.forename: Kurt
authors.initials: K
authors.lastname: Seetoo
authors.forename: Tracy
authors.initials: T
authors.lastname: Woodall
authors.forename: Rachel
authors.initials: R
authors.lastname: Wiseman
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Bialek
mesh_terms: D000293:Adolescent; D000328:Adult; D002644:Chickenpox / Q000453:epidemiology / Q000517:prevention & control; D019433:Chickenpox Vaccine / Q000008:administration & dosage / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks / Q000517:prevention & control / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D032541:Mass Vaccination / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D019433:Chickenpox Vaccine