Public Release: 

HPV vaccination not linked to riskier sex

Vaccine that prevents cancer-causing virus does not increase sexually transmitted infection rates

Harvard Medical School

Receiving the human papillomavirus vaccine does not increase rates of sexually transmitted infections (STIs) in adolescent females. The vaccine, which can prevent cervical cancer in women, has had a low uptake, partly because of concerns about how it will affect adolescent sexual activity.

The findings, based on investigations by researchers at Harvard Medical School and the University of Sothern California, published today in JAMA Internal Medicine, suggest that the vaccine does not promote risky sexual behaviors among those who have received the vaccine.

"Since this is one of the few medications ever developed that can actually prevent cancer, it's good to be able to reassure parents, physicians and policymakers that the vaccine does not promote unsafe sexual practices among girls and young women," said Anupam Jena, assistant professor of health care policy at HMS, internist at Massachusetts General Hospital and faculty research fellow at the National Bureau of Economic Research.

In Australia, which has instituted a national policy of mandatory HPV vaccination, delivered for free through the schools, more than 80 percent of girls ages 14-16 have received at least one of the three recommended doses of the vaccine. In the U.S., the same-dosage rate for girls ages 13-17 is 57.3 percent.

Two HPV vaccines currently exist in the market. When the first HPV vaccine, Gardasil, was introduced in 2006, there was outcry among some parents, pediatricians and politicians in the U.S. that vaccinating young girls might increase their chances of engaging in risky sexual activity, either through introducing the idea of sexual activity at an early age through prevaccination counseling or through creating a mistaken idea that the vaccine protects against more than just HPV.

These concerns spurred political controversies that led some states to ban mandatory HPV vaccination.

In the study, 21,000 girls who were vaccinated were matched with 186,000 unvaccinated girls who were the same age, who had the same insurance plan and who lived in the same geographic region of the United States. Rates of STIs were measured quarterly for a year before and a year after vaccination.

In both the vaccinated and unvaccinated groups, STIs increased at the same pace as the girls grew older. The vaccinated girls did have slightly higher STI rates both before and after vaccination when compared with the unvaccinated group, perhaps because girls choosing to receive the vaccine were more likely to already be sexually active than those choosing not to be vaccinated. However, the rate of increase in sexually transmitted infections was identical between vaccinated and unvaccinated females, which suggests that the girls' sexual behaviors were not altered in the least by the vaccine. Any behaviors resulting in infections that did occur were independent of the vaccine.

"If providing girls with the HPV vaccine caused an increase in risky sexual behavior, we would expect to have seen a steeper increase in STI rates in the quarters following administration of the vaccine. We found no such increase, causing us to conclude that there was no association between using the vaccine and unsafe sexual practices," said study co-author Seth Seabury, associate professor of research in the Department of Emergency Medicine at the Keck School of Medicine and a fellow in the Leonard D. Schaeffer Center for Health Policy and Economics at the University of Southern California.

Of the two HPV vaccines currently available, Ceravix and Gardasil, both prevent cervical cancer. Gardasil also protects against genital warts and anal cancer in both girls and boys and protects against vulvar cancer and vaginal cancer in girls. HPV vaccines offer the best protection to girls and boys before becoming sexually active with another person, according to the Centers for Disease Control and Prevention, which is why HPV vaccination is recommended for preteen girls and boys at age 11 or 12.

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This study was funded by grant 1DP50d017897-01 from the National Institutes of Health (Early Independence Award) and grant 5P01AG033559 from the National Institute on Aging.

Harvard Medical School has more than 7,500 full-time faculty working in 11 academic departments located at the School's Boston campus or in one of 47 hospital-based clinical departments at 16 Harvard-affiliated teaching hospitals and research institutes. Those affiliates include Beth Israel Deaconess Medical Center, Brigham and Women's Hospital, Cambridge Health Alliance, Boston Children's Hospital, Dana-Farber Cancer Institute, Harvard Pilgrim Health Care, Hebrew Senior Life, Joslin Diabetes Center, Judge Baker Children's Center, Massachusetts Eye and Ear Infirmary, Massachusetts General Hospital, McLean Hospital, Mount Auburn Hospital, Schepens Eye Research Institute, Spaulding Rehabilitation Hospital and VA Boston Healthcare System.

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