February 13, 2015 Kim Krisberg 0Comment

When the U.S. Food and Drug Administration approved the first vaccine to protect against cancers caused by certain strains of the human papillomavirus, or HPV, public health advocates cheered its arrival and life-saving potential. Unfortunately, the new vaccine quickly became embroiled in a debate over whether immunizing young girls against HPV, a sexually transmitted disease, would lead to risky sexual behavior. A new study, however, finds that the vaccine is not associated with an uptick in STDs — an indicator that HPV immunization does not promote unsafe sex.

To conduct the study, which was published in February in JAMA Internal Medicine, researchers analyzed an insurance database of young girls ages 12 to 18 from 2005 through 2010. They compared STD rates among girls who were vaccinated against HPV with those who were not — the eventual data set included more than 21,600 girls who received the vaccine and about 186,500 girls who were not vaccinated. While they found that young girls and women vaccinated against HPV typically had higher STD rates before and after immunization when compared to their unvaccinated peers, there was no significant difference in the growth of STD rates between the two groups in the year following vaccination. In other words, the study findings led researchers to conclude that the HPV vaccine is not likely associated with an increase in unsafe sexual behavior.

While previous research has examined the same question, study co-author Anupam Jena, an assistant professor of health care policy and medicine at Harvard Medical School and an assistant physician in the Department of Medicine at Massachusetts General Hospital, told me that this study is the first to examine such a large cohort of vaccinated and unvaccinated girls. Jena noted that HPV vaccination rates in the U.S. are quite low, with less than half of teen girls receiving all three doses of the vaccine. (Considering that this vaccine is the first-ever medical therapy that can prevent cancer, he described such low immunization rates as “somewhat shocking.”) Federal health officials currently recommend that boys and girls receive the vaccine at ages 11 or 12 years old.

Jenna added that prior surveys have found that significant percentages of parents, about 20 to 30 percent, as well as pediatricians, more than 10 percent, do voice personal concerns that HPV vaccination could tacitly approve the initiation of sexual activity or promote unsafe sexual behaviors.

“It’s this context that makes it such an important issue to understand,” he told me. “I think it’s a reasonable concern and not one to automatically dismiss. There are studies that do suggest that sometimes there are unintended consequences of well-intended (medical therapies), so it’s not unreasonable that this can occur. That’s why we turn to science to answer these questions.”

In addition to finding no evidence that HPV vaccination leads to higher rates of STDs, the study also revealed interesting differences and characteristics that could be useful in clinical and public health settings. For example, researchers found that girls and young women living in the South were less likely to be vaccinated. Overall, vaccination rates increased with age. Vaccinated females had higher rates of STDs before and after immunization when compared with unvaccinated females, and vaccinated females were also more likely to be sexually active in the year prior to immunization. Jena noted that these last two findings might be of particular interest to physicians when determining which patients are most in need of safe sex information.

Study authors Jena, Dana Goldman and Seth Seabury write:

We found that, although vaccinated females had higher STI (sexually transmitted infection) rates after vaccination compared with matched controls, these differences existed before vaccination as well. Our difference-in-difference analysis that compared changes in STI rates over time between vaccinated and nonvaccinated females found no evidence of an association between HPV vaccination and higher STI rates. Even among females who were more likely to be sexually active before HPV vaccination as measured by contraceptive medication use, there was no evidence of increased unsafe sexual behavior.

So, how can these findings translate in practice and enhance vaccine promotion and education? I posed this question to Jena, noting that previous messaging research has found that simply providing parents with corrective information on vaccine safety isn’t likely to change any minds (for an example, see this study). Jena said that while it’s true that this study won’t likely result in a sudden rush of girls being vaccinated against HPV, “I do think this kind of study can move the needle a little bit in a few ways.” One way is through media dissemination, he said, and another is by providing pediatricians with a little more leverage during conversations with parents who seem on the verge of saying “yes” to the HPV vaccine.

“What we’ve done is add information to what is already known and hopefully that will be useful,” Jena said. “At the end of the day, the real push is how do you translate that information into something tangible that can actually improve vaccination rates.”

For more on the HPV vaccine study, visit JAMA Internal Medicine or read this news release.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.

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