Some adolescent girls who get the HPV vaccine to prevent cervical cancer wrongly think they no longer need to practice safe sex, U.S. researchers said on Monday.
The study, published in the Archives of Pediatric & Adolescent Medicine, shows the need for better education about the vaccines and their limitations.
Merck's Gardasil and GlaxoSmithKline's Cervarix vaccines protect against strains of the humanpapilloma virus or HPV that cause cervical cancer. Gardasil also protects against some strains of the virus that cause genital warts.
But neither vaccine can prevent other forms of sexually transmitted diseases such as syphilis, gonorrhea or human immunodeficiency virus or HIV that causes AIDS.
And HPV vaccines can only prevent HPV infections; they do not treat active infections.
Most girls who get the vaccine know its limitations, the researchers said, but the vaccines are recommended for all girls aged 11 to 12, and overestimating their effect could increase a young woman's risk of contracting other sexually transmitted diseases.
For the study, Dr. Tanya Kowalczyk Mullins of Cincinnati Children's Hospital Medical Center and colleagues surveyed 339 girls aged 13 to 21 about their perceptions of risk after their first HPV vaccination. Several mothers also took part.
Overall, most adolescent girls said they believed it was important to practice safe sexual behaviors after getting the shot. But a small group of girls -- 23.6 percent -- believed they were less at risk for getting sexually transmitted diseases after getting the vaccine.
Factors associated with this view included having less information about the vaccine and about HPV infections, less concern about contracting HPV and lack of condom use at last sexual intercourse with a male partner.
The findings suggest doctors need to do a better job of educating girls and their mothers about the vaccine.
"Clinicians discussing HPV vaccination with girls and their mothers may need to emphasize the limitations of the vaccine and to specifically address that the vaccine does not prevent other sexually transmitted infections," the team wrote.
HPV is the most common sexually transmitted infection in the United States. More than half of U.S. adults will be exposed to the virus at some point during their lifetime.
The authors said the study was limited in that subjects came from a single urban clinic serving low-income clients so the findings may not apply to more general populations.
The study was funded by the National Institutes of Health, but some authors have been awarded research grants from Merck.