Kim Painter

Special to USA TODAY

Thanks to a vaccination program that began a decade ago, fewer U.S. women are entering adulthood infected with a sexually transmitted virus that can cause cancer, new research shows.

The study, published Monday in Pediatrics, is the first to show falling levels of dangerous strains of the human papillomavirus (HPV) among women in their early 20s. Researchers believe those women are the leading edge of a generation that should see fewer cases of cervical, vaginal, anal and throat cancers in the decades ahead.

Health officials have recommended vaccines against HPV for girls and young women since 2006 and for boys and young men since 2011.

Earlier reports showed infections starting to drop among teen girls, despite fairly low vaccination rates. The new report, from researchers at the federal Centers for Disease Control and Prevention, shows rates dropping in girls and women ages 14 to 24. Similar data on boys and young men are not yet available.

“We are seeing exactly what we would expect — that the first impact would be seen in the youngest age groups and, then as they age into the older age groups, we would see an impact on young women,” lead researcher Lauri Markowitz said. “But we would see greater impact with greater vaccine coverage.”

The study is based on interviews and medical tests conducted during the federal government’s National Health and Nutrition Examination Surveys in 2003-2006 (before the vaccines) and 2009-2012 (the most recent data available).

By the later period, about 51% of teen girls and 33% of women ages 20-24 had received at least one of the three recommended doses of the HPV vaccine. The vaccine is recommended for girls and boys ages 11-12. It can be given to women up to age 26 and men up to age 21.

The study found that after the vaccine became available, infection rates with targeted strains of HPV dropped to:

• 4.3% among all girls 14-19, down from 11.5%.

• 12.1% among all women 20-24, down from 18.5%.

• 2.1% among sexually active girls and women 14-24 who were vaccinated vs. 16.9% among those who were not.

“It means there’s going to be a whole lot less disease,” related to HPV, starting with fewer cases of genital warts and pre-cancers for women in their 20s, said Debbie Saslow, director of women’s cancer programs at the American Cancer Society. “Then 10 years later, that’s when we are going to start to see the cancers drop.”

The impact will be greater if HPV vaccines become as routine as other vaccines for children and teens, Saslow said. Some parents remain "vaccine hesitant," partly because of inaccurate reports of severe side effects, she said. But a bigger problem is that physicians do not seem to recommend vaccines for HPV vaccines as strongly as others, she added.

Markowitz said some doctors have not gotten the message that the vaccine will do the most good when given before teens become sexually active.

Dana Zillgitt, 25, of Dallas, said she remembers her pediatrician waving off her first questions about HPV vaccination nearly a decade ago. “The doctor was like, ‘You are just 16, you are just a child, you are not sexually active.' He just didn’t recommend it.”

Zillgitt said she eventually got vaccinated anyway, though she did not complete all three shots. She now wonders if that contributed to a recent health scare: she found out she was infected with HPV and had some abnormal cervical cells, but not cancer.

Studies suggest partial vaccination offers some protection. Zillgitt urges girls and women not to put off the vaccine.

“It’s a scary thing when the doctor says you have an (infection) that could potentially lead to cancer,” she wrote in a post on the website Twenty Something Living.