More teen girls are getting the human papillomavirus (HPV) vaccine, which protects against cervical, anal and other cancers, but the numbers are still  "unacceptably low", according to U.S. health officials.

The vaccine rate since its introduction in 2006 has flattened out after initial interest, with last year showing an increase from 33% to 38% of girls between 13 and 17 years of age having received the full three dose treatment.

The U.S. Centers for Disease Control and Prevention recommends all boys and girls aged 11 and 12 get the three-dose vaccine so that protection is in place before they become sexually active.

"We were disappointed with the overall findings," said said Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention. There is barely any improvement over last year, she said.

"It's frustrating to report almost the same HPV vaccination coverage levels among girls for another year," Schuchat added. "Pre-teens need HPV vaccine today to be protected from HPV cancers tomorrow."

The vaccine protects against human papillomavirus, or HPV. The sexually transmitted bug can cause cervical cancer, genital warts and other illnesses.

"When a teen (has been) in the doctor's office and received another vaccine but not HPV, that is a missed opportunity," Schuchat said. If every teen who got a vaccine received an HPV dose at the same time, 91 percent of eligible girls would have been vaccinated by now, CDC said.

Most school districts do not require HPV vaccine for attendance, but Schuchat said the real chance to make a difference lies with pediatricians. "We have very good coverage with the other vaccines and not all states require all of the vaccines, so the key, we think, is if they are in the doctor's office for something else and they have a chance to get vaccinated," Schuchat said.