Some girls may also perceive parental consent to HPV vaccination as authorization for sexual activity [12]. A large Swedish survey conducted in 2007 showed that 11% of parents worried that their child would have more unprotected sex or more partners if vaccinated against HPV, and a further 21% were undecided to the same question [13]. The concern that HPV vaccination may increase sexual risk taking may be a barrier to HPV vaccine uptake [14]. Previous studies have shown that most girls do not intend to change their sexual behaviour if vaccinated against HPV [15] and [16]. Several recent studies indicate that

the sexual behaviour of recipients and non-recipients of the HPV vaccine is similar ALK inhibitor [17], [18], [19], [20], [21] and [22], which is also supported by a study addressing outcomes related to sexual activity [23]. However, studies with large population-based samples and analyses that exclusively address

sexual behaviour occurring subsequent to HPV vaccination are lacking. Further investigations of potential associations between HPV vaccination and sexual behaviour are thus important to address the concerns expressed by some of those selleck chemicals involved in decisions regarding HPV vaccination. In the present study, we investigate whether women vaccinated against HPV before or at the same age as sexual debut differ from unvaccinated women in terms of subsequent sexual risk taking behaviour. We address age at first intercourse, non-use of contraception during first intercourse and the number of sexual partners among women in Denmark, Norway and Sweden in the settings of opportunistic vaccination and organized catch-up vaccination. A total sample of 83,720 women aged 18–45 was randomly enough selected from the population registries in Denmark, Norway and Sweden in 2011 (Table 1). Nordic population registries contain demographics about the entire population in the respective country, such as each citizen’s date of birth, sex, vital status and address [24] and [25].

The population registries are continually updated, and each citizen is identifiable by a unique personal identity number (PIN). All sampled women were invited to take part in the study, but 3167 women were not eligible because they: did not speak the local language (n = 1173), lived abroad during the time interval of response (n = 696), had a physical/mental disability (n = 120), died before contact (n = 11), or had an unknown address (n = 1167). Among the 80,553 women eligible for the study, 48,870 answered the questionnaire. We excluded 82 women due to a discrepancy between the registered PIN and the reported year of birth, giving a total of 48,788 study participants, and an overall participation rate of 60.6% (Table 1). Due to a lag between sampling and response, 158 women were 46 years old at response.