Study finds no link between HPV vaccination, increase in STIs

RESEARCHERS have demonstrated that human papillomavirus vaccination is not associated with an increase in sexually transmitted infections, offering reassurance that the vaccine does not promote risky sexual disinhibition.

      HPV vaccination can prevent cervical, vulvar and vaginal cancers, along with genital warts.

     In a new study, published in JAMA Internal Medicine, a group of researchers investigated sexually transmitted infection (STI) prevalence among females aged 12-18 using a large insurance database.

    The human papillomavirus (HPV) vaccine is known to prevent certain forms of cancer and genital warts caused by strains of what is the most common sexually transmitted infection.

    Around one-quarter of women in the US aged 14-19 and 45 per cent of women aged 20-24 are affected by HPV.

    Despite this level of prevalence, vaccination among women in the US is low. A three-dose series of the vaccine is recommended, yet, according to the authors, only 38 per cent of females aged 13 to 17 received the recommended dosage in 2013. A single dose was received by 57 per cent of females.

    Much attention has been paid to concerns that HPV vaccination could promote unsafe sexual activity. However, Medical News Today has previously reported on research demonstrating that HPV vaccination is not linked with risky sexual behavior in adolescent girls.

‘Reassuring findings’

    For the new study, the authors followed 208,111 females from 2005 through to 2010. Of these, 21,610 were females vaccinated against HPV and 186,501 were age-matched females who did not receive the vaccine.

    During this period, the authors found that vaccinated females were more likely to be sexually active in the year prior to receiving the HPV vaccination compared with the control group. Vaccinated females also had higher rates of STIs than the non-vaccinated participants, both before and after vaccination.

    In the year before vaccination, 4.3 per 1,000 of the vaccinated group developed an STI, compared with 2.8 per 1,000 of the non-vaccinated group. In the year after vaccination, these rates increased to 6.8 per 1,000 and 4.2 per 1,000 for each group respectively.

   However, the difference-in-difference odds ratio for contracting an STI between the two groups implies that HPV vaccination was not associated with a relative increase in the rate of STIs. Although the vaccinated females had a higher STI rate than the age-matched controls, this difference existed prior to vaccination.

     The study is subject to a number of limitations. The participants were all privately insured and findings related to this demographic group might not be applicable to the wider public. Also, STIs and vaccinations were solely measured through insurance claims – these figures may, therefore, include testing rather than just confirmed infections and may miss visits to anonymous clinics.

    Finally, STIs are only one measure of unsafe sexual activity. The authors suggest that this could be alternatively assessed through questionnaires about condom use and number of sexual partners.

Findings ‘should not come as a surprise’

    “We found no evidence that HPV vaccination leads to higher rates of STIs,” conclude the authors. “Given low rates of HPV vaccination among adolescent females in the United States, our findings should be reassuring to physicians, parents and policy makers that HPV vaccination is unlikely to promote unsafe sexual activity.”