title: Varicella Vaccine Effectiveness in Preventing Community Transmission in the 2-Dose Era.
abstract: OBJECTIVE
  We examined overall and incremental effectiveness of 2-dose varicella vaccination in preventing community transmission of varicella among children aged 4 to 18 years in 2 active surveillance sites. One-dose varicella vaccine effectiveness (VE) was examined in those aged 1 to 18 years.
  
  
  METHODS
  From May 2009 through June 2011, varicella cases identified during active surveillance in Antelope Valley, CA and Philadelphia, PA were enrolled into a matched case-control study. Matched controls within 2 years of the patient's age were selected from immunization registries. A standardized questionnaire was administered to participants' parents, and varicella vaccination history was obtained from health care provider, immunization registry, or parent records. We used conditional logistic regression to estimate varicella VE against clinically diagnosed and laboratory-confirmed varicella.
  
  
  RESULTS
  A total of 125 clinically diagnosed varicella cases and 408 matched controls were enrolled. Twenty-nine cases were laboratory confirmed. One-dose VE (1-dose versus unvaccinated) was 75.6% (95% confidence interval [CI], 38.7%-90.3%) in preventing any clinically diagnosed varicella and 78.1% (95% CI, 12.7%-94.5%) against moderate or severe, clinically diagnosed disease (≥50 lesions). Among subjects aged ≥4 years, 2-dose VE (2-dose versus unvaccinated) was 93.6% (95% CI, 75.6%-98.3%) against any varicella and 97.9% (95% CI, 83.0%-99.7%) against moderate or severe varicella. Incremental effectiveness (2-dose versus 1-dose) was 87.5% against clinically diagnosed varicella and 97.3% against laboratory-confirmed varicella.
  
  
  CONCLUSIONS
  Two-dose varicella vaccination offered better protection against varicella from community transmission among school-aged children compared with 1-dose vaccination.
authors.affiliation: Philadelphia Department of Public Health, Philadelphia, Pennsylvania; dana.perella@phila.gov.
authors.forename: Dana
authors.initials: D
authors.lastname: Perella
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia;
authors.forename: Chengbin
authors.initials: C
authors.lastname: Wang
authors.affiliation: Los Angeles County Department of Public Health, Los Angeles, California; and.
authors.forename: Rachel
authors.initials: R
authors.lastname: Civen
authors.affiliation: Philadelphia Department of Public Health, Philadelphia, Pennsylvania;
authors.forename: Kendra
authors.initials: K
authors.lastname: Viner
authors.affiliation: Los Angeles County Department of Public Health, Los Angeles, California; and.
authors.forename: Karen
authors.initials: K
authors.lastname: Kuguru
authors.affiliation: Philadelphia Department of Public Health, Philadelphia, Pennsylvania;
authors.forename: Irini
authors.initials: I
authors.lastname: Daskalaki
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia;
authors.forename: D Scott
authors.initials: DS
authors.lastname: Schmid
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia;
authors.forename: Adriana S
authors.initials: AS
authors.lastname: Lopez
authors.affiliation: Southern California Permanente Medical Group, Kaiser Permanente, Pasadena, California.
authors.forename: Hung Fu
authors.initials: HF
authors.lastname: Tseng
authors.affiliation: Philadelphia Department of Public Health, Philadelphia, Pennsylvania;
authors.forename: E Claire
authors.initials: EC
authors.lastname: Newbern
authors.affiliation: Los Angeles County Department of Public Health, Los Angeles, California; and.
authors.forename: Laurene
authors.initials: L
authors.lastname: Mascola
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia;
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Bialek
mesh_terms: D000293:Adolescent; D002140:California / Q000453:epidemiology; D016022:Case-Control Studies; D002644:Chickenpox / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission; D019433:Chickenpox Vaccine / Q000008:administration & dosage*; D002648:Child; D002675:Child, Preschool; D017714:Community-Acquired Infections / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission; D018562:Disease Transmission, Infectious / Q000517:prevention & control; D005260:Female; D006801:Humans; D007117:Immunization, Secondary; D008297:Male; D015143:Philadelphia / Q000453:epidemiology; D011159:Population Surveillance; D012307:Risk Factors; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires
chemical_list: D019433:Chickenpox Vaccine