title: Quadrivalent human papillomavirus vaccine effectiveness: a Swedish national cohort study.
abstract: BACKGROUND
  Incidence of condyloma, or genital warts (GW), is the earliest possible disease outcome to measure when assessing the effectiveness of human papillomavirus (HPV) vaccination strategies. Efficacy trials that follow prespecified inclusion and exclusion criteria may not be fully generalizable to real-life HPV vaccination programs, which target a broader segment of the population. We assessed GW incidence after on-demand vaccination with quadrivalent HPV vaccine using individual-level data from the entire Swedish population.
  
  
  METHODS
  An open cohort of girls and women aged 10 to 44 years living in Sweden between 2006 and 2010 (N > 2.2 million) was linked to multiple population registers to identify incident GW in relation to HPV vaccination. For vaccine effectiveness, incidence rate ratios of GW were estimated using time-to-event analyses with adjustment for attained age and parental education level, stratifying on age at first vaccination.
  
  
  RESULTS
  A total of 124 000 girls and women were vaccinated between 2006 and 2010. Girls and women with at least one university-educated parent were 15 times more likely to be vaccinated before age 20 years than girls and women whose parents did not complete high school (relative risk ratio = 15.45, 95% confidence interval [CI] = 14.65 to 16.30). Among those aged older than 20 years, GW rates declined among the unvaccinated, suggesting that HPV vaccines were preferentially used by women at high risk of GW. Vaccination effectiveness was 76% (95% CI = 73% to 79%) among those who received three doses of the vaccine with their first dose before age 20 years. Vaccine effectiveness was highest in girls vaccinated before age 14 years (effectiveness = 93%, 95% CI = 73% to 98%).
  
  
  CONCLUSIONS
  Young age at first vaccination is imperative for maximizing quadrivalent HPV vaccine effectiveness.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, P.O. Box 281, SE-171 77 Stockholm, Sweden.
authors.forename: Amy
authors.initials: A
authors.lastname: Leval
authors.forename: Eva
authors.initials: E
authors.lastname: Herweijer
authors.forename: Alexander
authors.initials: A
authors.lastname: Ploner
authors.forename: Sandra
authors.initials: S
authors.lastname: Eloranta
authors.forename: Julia
authors.initials: J
authors.lastname: Fridman Simard
authors.forename: Joakim
authors.initials: J
authors.lastname: Dillner
authors.forename: Cecilia
authors.initials: C
authors.lastname: Young
authors.forename: Eva
authors.initials: E
authors.lastname: Netterlid
authors.forename: Pär
authors.initials: P
authors.lastname: Sparén
authors.forename: Lisen
authors.initials: L
authors.lastname: Arnheim-Dahlström
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D052685:Alphapapillomavirus / Q000276:immunology; D002648:Child; D015331:Cohort Studies; D003218:Condylomata Acuminata / Q000453:epidemiology* / Q000517:prevention & control* / Q000821:virology; D015986:Confounding Factors, Epidemiologic; D005260:Female; D006801:Humans; D015994:Incidence; D016017:Odds Ratio; D030361:Papillomavirus Infections / Q000453:epidemiology* / Q000517:prevention & control* / Q000821:virology; D053918:Papillomavirus Vaccines / Q000008:administration & dosage*; D012042:Registries; D012959:Socioeconomic Factors; D013548:Sweden / Q000453:epidemiology; D016896:Treatment Outcome
chemical_list: D053918:Papillomavirus Vaccines