title: Dose-Related Differences in Effectiveness of Human Papillomavirus Vaccination Against Genital Warts: A Nationwide Study of 550,000 Young Girls.
abstract: BACKGROUND
  Reducing the number of doses in the human papillomavirus (HPV) vaccination regimen from 3 to 2 could increase coverage rates. In this cohort study, we assessed the risk of genital warts (GWs) according to timing and number of doses of quadrivalent HPV vaccine.
  
  
  METHODS
  From population-based registries, we identified all girls in Denmark born during 1985-1999, for whom information on HPV vaccinations was retrieved. The cohort was followed for GW occurrence during 2006-2012. Incidence rate ratios (IRRs) were calculated by Poisson regression to determine differences in GW rates by number of vaccine doses.
  
  
  RESULTS
  Of the 550,690 girls in the cohort, 361 734 had been vaccinated. Of these, 25.9% had been vaccinated twice and 58.8% 3 times. The risk of GWs decreased significantly with each additional dose of vaccine. For girls who received 2 doses, extension of the interval between doses reduced the incidence of GWs. In comparison with a 2-month interval, the incidence of GWs was reduced by 45% (95% confidence interval [CI], 20%-62%), 55% (95% CI, 35%-69%), and 63% (95% CI, 44%-75%), with an interval of 4, 5, and 6 months, respectively. The IRR of 2 vs 3 doses was close to 1, with an interval of about 6 months between the first 2 doses.
  
  
  CONCLUSIONS
  With the original vaccine schedule, completion of 3 doses seems to be required to obtain full protection against GWs. A 2-dose regimen may be as effective if the dosing interval is extended to around 6 months, although the long-term effectiveness of this regimen is unknown.
authors.affiliation: Virus, Lifestyle and Genes.
authors.forename: Maria
authors.initials: M
authors.lastname: Blomberg
authors.affiliation: Statistics, Bioinformatics and Registry, Danish Cancer Society Research Centre.
authors.forename: Christian
authors.initials: C
authors.lastname: Dehlendorff
authors.affiliation: Department of Dermato-Venereology, Bispebjerg Hospital.
authors.forename: Carsten
authors.initials: C
authors.lastname: Sand
authors.affiliation: Virus, Lifestyle and Genes Department of Gynaecology, Rigshospitalet, University of Copenhagen, Denmark.
authors.forename: Susanne K
authors.initials: SK
authors.lastname: Kjaer
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D003218:Condylomata Acuminata / Q000453:epidemiology* / Q000517:prevention & control*; D003718:Denmark / Q000453:epidemiology; D004306:Dose-Response Relationship, Immunologic; D005260:Female; D006801:Humans; D032541:Mass Vaccination / Q000706:statistics & numerical data; D053918:Papillomavirus Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D055815:Young Adult
chemical_list: D053918:Papillomavirus Vaccines
keywords: condyloma acuminata; dose–response relationship; genital warts; human papillomavirus; vaccination