Harvard University. US: 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 Southern 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.
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“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.
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.