In a move that could boost HPV vaccination rates, the U.S. Centers for Disease Control and Prevention on Wednesday said younger adolescents need only two doses of the vaccine, rather than three as previously recommended.

The human papillomavirus vaccine (HPV), introduced a decade ago, was hailed as a breakthrough in cancer prevention because it wards off infection with sexually-transmitted strains of the virus that cause cervical cancer and some rarer head, neck and genital cancers.  But doctors and parents of adolescents have been slow to embrace the immunization, put off by its novelty, link to sexual activity, and the complexity of the three-shot regimen, which is covered by insurance.

The Advisory Committee on Immunization Practices, which counsels the CDC on vaccinations, voted to Wednesday to make the change to two doses. CDC director Tom Frieden accepted the recommendation hours later.

The change fits with the Food and Drug Administration's approval earlier this month of a 2-dose schedule for younger adolescents who get the improved version of Merck's Gardasil vaccine. The new version protects against nine cancer-causing strains of HPV (the original protected against four) plus strains that cause genital warts. Gardasil is the most widely used HPV vaccine, but GlaxoSmithKline markets Cervarix, which does not protect against genital warts.

Under the new schedule, the first of two shots of the HPV vaccine should be administered to boys and girls at ages 11 or 12, although it could be given as early as age 9, as under the previous guidance. The second shot would be given six to 12 months after the first shot.

The new recommendation says young people who get vaccinated between ages 15 and 26 should continue to get three shots to build an adequate immune response against the virus.

HPV vaccination rates have been improving, but remain far below that of other childhood vaccines. Last year, about half of boys and 63 percent of girls ages 13 to 17 had gotten at least one HPV shot. Only 13 percent of boys and 37 percent of boys had gotten all three doses.

"By reducing the number of doses needed to complete HPV vaccination, it should lead to an increase in the percentage of eligible boys and girls who get vaccinated," said Douglas Lowy, acting director of the National Cancer Institute. Lowy and his NCI colleague John Schiller developed the technology that underlies the HPV vaccine.

The CDC says that about 80 million Americans are infected with HPV; in most cases, the immune system clears the infection. Still, more than 38,000 cases of HPV-associated cancers occur in the United States every year.

The Washington Post contributed to this report.