A little over half of US girls ages 13 to 17 have not gotten even one dose of the HPV vaccine, and among the main reasons are poor awareness and the failure of doctors to recommend vaccination, a study shows.

Despite the millions Merck and GSK have spent advertising Gardasil and Cervarix over the past five years, a lack of knowledge about the vaccine was the top reason given by parents who said they did not intend to have their daughters vaccinated, according to an analysis of data from the 2008 and 2009 National Immunization Survey-Teen published in Pediatrics, the journal of the American Academy of Pediatrics.

While 19.4% of those parents said they didn’t know about HPV vaccines, similar proportions said the vaccine was unneeded (18.8%) or that their daughters were not sexually active (18.3%), and 13.1% said they did not receive a provider recommendation.

“We do know that a strong physician recommendation is very important in the decision-making process for consumers when it comes to vaccines,” said Merck spokesperson Jennifer Allen Woodruff. “And managed care coverage is still coming up to speed. That’s certainly a factor,” though less so for Gardasil, she added.

Of those who did initiate the vaccine, only half got all three doses, and while the study found no differences in initiation by race or ethnicity, fewer Black and Hispanic girls completed the series, and income and insurance status were “significantly associated” with initiation.

“Despite [Vaccines for Children program] eligibility, uninsured girls had the lowest vaccination initiation rate,” said the study. “Lack of insurance is a known risk factor for lack of preventive health care among adolescents and low vaccination rates among young children.”

The high cost of the vaccines may be deterring doctors from stocking them, the study’s authors suggested, noting that at an average of $130 a dose in the private sector, Cervarix and Gardasil are among the most expensive vaccines.

“Because of costs and concerns bout reimbursement, some providers might not stock or offer the vaccine, which might contribute to lower vaccination rates among non-VFC eligible girls,” they wrote.

Their recommendations include: increasing insurance access and awareness of the VFC program; encouraging providers to recommend vaccination for girls in that age group; participation in registries and use of reminder/recall systems to remind parents, patients and providers when doses are due and reach those patients who are overdue; and educating parents on the disease risks and the benefits of vaccination before exposure.

Overall, 32% of US girls ages 13-17 completed the three-dose course in 2010 (actually, the CDC recommends that girls be vaccinated at ages 11-12, and considers the 13-17 cohort a “catch-up” group). By contrast, completion rates are above 80% in some parts of Canada for girls in the targeted age group. Coverage is increasing in the US, but slowly.

Merck spent $339 million in measured media promoting Gardasil from its introduction in 2006 to December of last year, according to Nielsen data. GSK has spent considerably less promoting Cervarix, approved in 2009, to consumers, but both companies have directed heavy sales efforts at healthcare professionals.