Population-level sexual behaviours in adolescent girls before and after introduction of the human papillomavirus vaccine (2003–2013)
Menée en Colombie-Britannique à partir des données de trois enquêtes réalisées en 2003, 2008 et 2013 auprès de 298 265 adolescentes hétérosexuelles, cette étude analyse les comportements sexuels des adolescentes avant et après l'introduction en 2008 d'un programme de vaccination contre le papillomavirus humain ciblant les écolières et collégiennes âgées de 9 à 13 ans
BACKGROUND : The human papillomavirus (HPV) vaccine is delivered widely through school-based immunization programs. Some groups have expressed concern that HPV vaccination programs will result in an increase in sexual risk-taking behaviours among adolescents. We aimed to evaluate population-level changes in sexual behaviours before and after implementation of the school-based HPV vaccination program in British Columbia. METHODS : In 2008, a school-based HPV vaccination program for girls was introduced in British Columbia. Using data from the BC Adolescent Health Survey — a longitudinal provincial survey administered in schools to capture adolescent physical and emotional health indicators, we conducted a linear trend analysis on sexual health behaviours and risk factors in adolescent girls before and after the implementation of vaccination for HPV (2003, 2008 and 2013). RESULTS : We analyzed data for 298 265 girls who self-identified as heterosexual. The proportion of girls reporting ever having sexual intercourse decreased from 21.3% (2003) to 18.3% (2013; adjusted odds ratio [OR] 0.79). Self-report of sexual intercourse before the age of 14 years decreased significantly from 2008 to 2013 (adjusted OR 0.76), as did reported substance use before intercourse (adjusted OR for 2003–2013 0.69). There was no significant change in the number of sexual partners reported (2003–2013). Between 2003 and 2013, girls’ reported use of contraception and condoms increased, while pregnancy rates decreased. INTERPRETATION : Since the implementation of school-based HPV vaccination program in BC, sexual risk behaviours reported by adolescent girls either reduced or stayed the same. These findings contribute evidence against any association between HPV vaccination and risky sexual behaviours. Human papillomavirus (HPV) is the most commonly diagnosed sexually transmitted infection in the world.1 While the majority of HPV infections are transient and resolve naturally without intervention, persistent infection with high-risk types of HPV can cause precancerous lesions that may progress to cervical, anal, oropharyngeal or other reproductive tract cancers, or anogenital warts if left untreated.2 There is evidence that vaccination programs for HPV effectively reduce rates of high-risk types of HPV at the population and clinical level.3,4 Cervarix (GlaxoSmithKline), Gardasil and Gardasil-9 (Merck) are the 3 vaccines approved by Health Canada5 and recommended for use by the Canadian National Advisory Committee on Immunization.6 All 3 vaccines protect against HPV types 16 and 18, which are responsible for 70% of all cervical cancers.2 Gardasil and Gardasil-9 reduce the risk of additional types of HPV that are associated with genital warts and other cancers. Many countries have implemented national publicly funded immunization programs for HPV. These programs are offered typically in school to adolescent girls aged 9–13 years and, in recent years, to boys.7 School-based programs for HPV vaccination have shown broad coverage among adolescent populations compared with other approaches.8 However, negative beliefs about HPV vaccination may present barriers to uptake. Parents of adolescent girls have expressed concern that HPV vaccination at a young age would encourage risky sexual behaviours such as early sexual debut, more sexual partners or unprotected intercourse,9–11 and that by consenting to having their child receive the HPV vaccine that they would be condoning sexual activity at younger ages.12 Some evidence from clinic-based populations, billings by physicians and cross-sectional studies of existing cohorts suggests no association between HPV vaccination and increased sexual risk behaviours after vaccination.13–15 However, few studies have examined population-level sexual behaviours over time. In this study, we used an established provincial adolescent health survey to evaluate population-level changes in sexual health and risky behaviours over a decade, before and after the implementation of the school-based HPV vaccination program, in British Columbia, Canada.