title: Effect of human papillomavirus (HPV) vaccination on clinical indicators of sexual behaviour among adolescent girls: the Ontario Grade 8 HPV Vaccine Cohort Study.
abstract: BACKGROUND
  Suboptimal human papillomavirus (HPV) vaccine coverage in some jurisdictions is partly attributed to fears that vaccination may increase risky sexual behaviour. We assessed the effect of HPV vaccination on clinical indicators of sexual behaviour among adolescent girls in Ontario.
  
  
  METHODS
  Using Ontario's administrative health databases, we identified a population-based cohort of girls in grade 8 in the 2 years before (2005/06 and 2006/07) and after (2007/08 and 2008/09) implementation of Ontario's grade 8 HPV vaccination program. For each girl, we then obtained data on vaccine receipt in grades 8 and 9 and data on indicators of sexual behaviour (pregnancy and non-HPV-related sexually transmitted infections) in grades 10-12. Using a quasi-experimental method known as regression discontinuity, we estimated, for each outcome, the risk difference (RD) and relative risk (RR) attributable to vaccination and to program eligibility.
  
  
  RESULTS
  The cohort comprised 260 493 girls, of whom 131 781 were ineligible for the program and 128 712 were eligible. We identified 15 441 (5.9%) cases of pregnancy and sexually transmitted infection and found no evidence that vaccination increased the risk of this composite outcome: RD per 1000 girls -0.61 (95% confidence interval [CI] -10.71 to 9.49) and RR 0.96 (95% CI 0.81 to 1.14). Similarly, we found no discernible effect of program eligibility: RD per 1000 girls -0.25 (95% CI -4.35 to 3.85) and RR 0.99 (95% CI 0.93 to 1.06). The findings were similar when outcomes were assessed separately.
  
  
  CONCLUSIONS
  We present strong evidence that HPV vaccination does not have any significant effect on clinical indicators of sexual behaviour among adolescent girls. These results suggest that concerns over increased promiscuity following HPV vaccination are unwarranted and should not deter from vaccinating at a young age.
authors.affiliation: Department of Epidemiology, Biostatistics, and Occupational Health (Smith, Kaufman, Strumpf), McGill University, Montréal, Que.; Department of Public Health Sciences (Lévesque), Queen's University, Kingston, Ont. leah.smith3@mail.mcgill.ca.
authors.forename: Leah M
authors.initials: LM
authors.lastname: Smith
authors.affiliation: Department of Epidemiology, Biostatistics, and Occupational Health (Smith, Kaufman, Strumpf), McGill University, Montréal, Que.; Department of Public Health Sciences (Lévesque), Queen's University, Kingston, Ont.
authors.forename: Jay S
authors.initials: JS
authors.lastname: Kaufman
authors.affiliation: Department of Epidemiology, Biostatistics, and Occupational Health (Smith, Kaufman, Strumpf), McGill University, Montréal, Que.; Department of Public Health Sciences (Lévesque), Queen's University, Kingston, Ont.
authors.forename: Erin C
authors.initials: EC
authors.lastname: Strumpf
authors.affiliation: Department of Epidemiology, Biostatistics, and Occupational Health (Smith, Kaufman, Strumpf), McGill University, Montréal, Que.; Department of Public Health Sciences (Lévesque), Queen's University, Kingston, Ont.
authors.forename: Linda E
authors.initials: LE
authors.lastname: Lévesque
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D009864:Ontario / Q000453:epidemiology; D030361:Papillomavirus Infections / Q000453:epidemiology / Q000517:prevention & control; D053918:Papillomavirus Vaccines; D010342:Patient Acceptance of Health Care / Q000523:psychology / Q000706:statistics & numerical data; D011247:Pregnancy; D011253:Pregnancy in Adolescence / Q000706:statistics & numerical data*; D012725:Sexual Behavior; D012749:Sexually Transmitted Diseases / Q000453:epidemiology* / Q000517:prevention & control; D014611:Vaccination / Q000523:psychology*
chemical_list: D053918:Papillomavirus Vaccines