Parents who go online to find out about the vaccine for human papillomavirus (HPV), a sexually transmitted disease that causes cervical cancer, may have a hard time finding accurate information, a recent U.S. study suggests.

In the U.S., the HPV vaccine is recommended for children at age 11 or 12 years, with the goal of protecting them against the virus before they become sexually active, and also for teens and young adults who may not have previously been vaccinated.

But many girls and boys don't receive the vaccine, at least in part because their parents may question whether it's necessary to protect them against a sexually transmitted disease at an age when they think children shouldn't be having sex.

The Internet, where the vast majority of Americans go for answers to a wide variety of medical questions, may be particularly misleading when it comes to facts about HPV, researchers report in the Journal of Adolescent Health.

When they searched for facts about this vaccine online, they found the top five to 10 results contained critical information only about a third of the time.

"In general, web pages that were against rather than neutral or supportive of HPV vaccination were of lower quality and had less complete information," said lead study author Dr. Linda Fu, a pediatrician at Children's National Health System and George Washington University in Washington, D.C.

"When web pages with inaccurate or incomplete medical information are ranked highly by search engines, there's a greater chance that more people are going to view them, which means they will stay highly ranked and continue to perpetuate misinformation," Fu added by email.

To assess the accuracy of web pages about HPV, Fu and colleagues did twenty separate searches using different terms that yielded 116 unique web pages.

Overall, 39 percent of these pages were critical of the vaccine, highlighting concerns about death or severe side effects, encouraging sexual activity or insufficient research.

Neutral search terms like "HPV vaccine" and "cervical cancer vaccine" turned up fewer negative pages in the top-ranked results than searches including words like "dangers" and "risks."

Researchers also assessed web pages based on how prominently they featured key facts about HPV, the vaccine and the cancers it's designed to prevent.

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Most of the pages mentioned cervical cancer, but fewer than half had information about other HPV-related diseases like genital and anal tumors, head and neck cancers or genital warts. Pages that didn't criticize the vaccine were more likely to mention these other diseases.

About half of the pages explained who should get the vaccine, but fewer offered information on how to get vaccinated or what it might cost.

One drawback of the study is that the researchers didn't have data on which exact search terms consumers most often use to learn about the HPV vaccine. People who are more hesitant about vaccination might also use more negative search terms that find content that matches their concerns, the researchers note.

"If you are looking for something specific, you are likely to find it on the Internet," Zeev Rosberger, a cancer researcher at McGill University in Quebec who wasn't involved in the study, said by email.

The findings confirm that it's best to get answers to medical questions directly from physicians, said Vetta Sanders Thompson, a researcher at Washington University in St. Louis who wasn't involved in the study.

"Individuals with a usual source of care and a relationship with a physician may have fewer questions and concerns and we know that they have less uncertainty about the vaccine," Thompson said by email. "They may be less likely to search for additional information."