FRIDAY, Jan. 23, 2015 (HealthDay News) — Only about half of American girls begin receiving the human papillomavirus (HPV) vaccine at the recommended age, a new study finds.

HPV is believed to cause nearly all cases of cervical cancer, and also other types of cancers and genital warts. The HPV vaccine protects against 70 percent of cervical cancers and 90 percent of genital warts cases, according to the researchers.

Girls should begin getting the three-dose HPV vaccine when they are 11 or 12. The vaccine is most effective before girls become sexually active, according to the U.S. Centers for Disease Control and Prevention. The CDC also recommends the vaccine for boys beginning at ages 11 or 12. However, the current study only looked at girls.

“Rates of HPV infection increase significantly every year for young people between 14 and 24, so vaccination at a young age is very important,” team leader Dr. Mahbubur Rahman in a University of Texas Medical Branch at Galveston, said in a news release. He is an associate professor in the obstetrics and gynecology department at the university.

The study found that the number of girls in the United States who started the vaccine series at the recommended age was 14 percent in 2008. By 2012, that number was 56 percent. The trends did not differ by race or ethnicity, according to the study published in the journal Vaccine.

The findings showed that nearly half of adolescent girls receive the vaccine after age 12 — and researchers said it’s not certain how effective the vaccine is after this age.

“It’s important that parents and health care providers are aware of the importance of early HPV vaccination to ensure that girls receive this vaccination at the CDC’s recommended age,” Rahman added.

— Robert Preidt

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SOURCE: University of Texas Medical Branch at Galveston, news release, Jan. 21, 2015