Once more with feeling: The HPV vaccine doesn’t make girls more likely to get pregnant or get an STI

From the CMAJ, “Effect of human papillomavirus (HPV) vaccination on clinical indicators of sexual behaviour among adolescent girls: the Ontario Grade 8 HPV Vaccine Cohort Study“:

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.

There are people who make an argument that if we vaccinate girls against a sexually transmitted infection, they will be more likely to have sex. I’ve covered this before. This study made use of Ontario’s administrative health database before and after the grade 8 HPV vaccination program was begun. The researchers looked at whether a girl was vaccinated, and then looked at pregnancy and STIs in them. They controlled for a ton of stuff.

There were more than 260,000 girls in the study, almost evenly split between girls who were eligible for the vaccine, once the program began, and those who weer ineligible, because they were in 8th grade before it went into effect. Just over half of “eligible” girls got the vaccine, but only 1% of “ineligible” girls got it. So there’s a clear difference.

In the study period, there were 15,441 pregnancies and sexually transmitted infections, affecting 5.9% of the girls. There was no relationship between getting the vaccine and having one of these outcomes, though. There was also no relationship between being in the “eligible” or “ineligible” group and having a bad outcome. There was no difference when they were analyzed together or separately.

The conclusion:

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.



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