Most teenagers aren’t getting vaccinated against human papillomavirus (HPV), and it’s their doctors’ fault.

While 70 percent of teenagers have been vaccinated against meningitis and 88 percent got the Tdap shot (against tetanus, diphtheria, and pertussis), a paltry 40 percent of females and 22 percent of males in the United States have been fully vaccinated against HPV.

Part of the hurdle with HPV vaccines is that full inoculation requires three rounds of shots. It also doesn’t help that pediatricians who are explaining HPV have to utter the dreaded words “sexually transmitted” to explain how the virus can lead to at least nine types of cancer.

Recommendations from the Centers for Disease Control and Prevention (CDC) say that teens should begin the three-shot HPV series at age 11 or 12, when they also receive the meningococcal and Tdap vaccines.

The vaccine is covered by almost all health insurance plans. It prevents nine types of cancer, including cervical cancer, as well as genital warts. Preteens aren’t toddlers — most can handle an extra shot without a meltdown. So what gives?

Research has repeatedly demonstrated that one of the strongest predictors of voluntary vaccination is a physician’s recommendation. If a doctor says get the vaccine, most people (or parents) will bite the bullet and get the shot, trusting that their healthcare provider knows how to best protect them (or their children) from preventable diseases.

Read More: Learn More About HPV Infection »

What Doctors Aren’t Saying

A team of public health researchers led by Melissa B. Gilkey of Harvard Medical School recently looked into the quality of provider recommendations for getting the HPV vaccine.

In a study published in Cancer Epidemiology, Biomarkers & Prevention this week, their results are telling: One in four physicians rate their own endorsement of the vaccine as weak.

Gilkey and her team also found that many providers’ failure to recommend the vaccine on time — that is, at the target age of 11 or 12 — contributes to missed opportunities for vaccination. Providers admitted to not recommending the vaccine in a timely manner (or not recommending it at all) for almost 40 percent of male patients and 26 percent of females, even though there are no known risks to administering the vaccine at that age.

“There are no known benefits to delaying HPV vaccination, but there are known costs,” Gilkey told Healthline.

Almost 60 percent of doctors reported using a “risk-based” approach to recommending the vaccine. For example, they might only recommend it if the teen was known to be sexually active or had a previous sexually transmitted infection. That practice is in direct conflict with CDC recommendations that all preteens receive the vaccine prior to initiating sexual activity.

HPV is spread through skin contact, not through vaginal secretions or semen, which means it can be spread by fingers, mouths, and virtually any part of the body.

Though the vaccine can still be effective after sexual contact has occurred, vaccinating children at a younger age is a better guarantee of cancer prevention than hoping a sexually active individual has not yet been exposed to one of the four strains of HPV prevented by the vaccine, or that a young person will delay sexual activity because they haven’t been vaccinated

In the Gilkey study, more than half of the physicians surveyed didn’t recommend vaccination at the same time they recommended the meningitis and Tdap vaccines, as is recommended by the CDC.

“Almost every state has a Tdap requirement for middle school entry,” explains Shannon Stokley, an epidemiologist in the CDC’s Immunization Services Division.As we know, missed opportunities for HPV are very common. If providers would administer HPV vaccine when they give other recommended vaccines, roughly 91 percent of 13-year-old girls would have received the first dose of HPV vaccine.”

Read More: Only One State Currently Requires HPV Vaccinations »

Why Doctors Aren’t Talking

Gilkey’s study found that unenthusiastic recommendations are about as effective as not mentioning the vaccine at all.

“Of the five communication practices we assessed, about half of physicians reported two or more practices that likely discourage timely HPV vaccination,” Gilkey said in a press release. “We are currently missing many opportunities to protect today’s young people from future HPV-related cancers.”

Many factors contribute to unproductive doctor-patient communication about HPV. The recommendations from the CDC have changed since the vaccine was first approved in 2006. And doctors who think a parent is uncomfortable with the conversation about HPV will sometimes give an incomplete or lukewarm endorsement of the vaccine. But Gilkey says those doctors may be reading the parents wrong.

“Prior research indicates that providers sometimes overestimate parents’ concerns. Some parents have no concerns and others simply want more information before making a decision,” Gilkey said. “Cancer prevention is an important goal for parents and the qualitative literature suggests that many parents appreciate getting a straight-forward, unambiguous recommendation for HPV vaccination.”

Read More: HPV Vaccine Doesn’t Lead to Unsafe Sex »

Getting Better at Giving Advice

Advocates are working to improve vaccination rates by helping doctors speak openly and effectively about the necessity of HPV vaccination.

Strategies include educating providers to lead with the idea of cancer prevention, finding ways to efficiently include the conversation in a brief clinic visit, and building provider confidence when discussing the benefits of the vaccine.

The CDC has also partnered with cancer organizations to educate parents about the vaccine’s benefits.

“We believe that providers can be more optimistic about recommending HPV vaccination,” Gilkey said. “Providers can deliver high-quality recommendations by saying the HPV vaccine is important, recommending it ‘on time’ by age 12 to all adolescents, and recommending same-day vaccination.”