PHILADELPHIA (CBS) — The Centers for Disease Control is on a mission to increase the number of boys and girls getting the HPV vaccine to prevent cancer.

Nationally, only about half of the young boys and girls have received the HPV vaccinations, but Philadelphia has the highest compliance rate in the country, according to national statistics. Melinda Wharton, director of the Immunization Services Division of the CDC says one issue is the shots must be given before the patient is sexually active.

“Talking about the vaccine has made physicians and parents uncomfortable, because HPV is transmitted by sexual contact,” Wharton says, “but, you know, we don’t get into big discussions about droplet transmission before we give the meningococcal congregate vaccine.”

She says the nationwide education campaign on the state and local level is having a positive impact.

“We are cautiously optimistic that we understand how to do better with HPV vaccination now,” Wharton says, “and it really does take for providers to see that it’s their responsibility to protect their patients from these cancers.”