Despite a complicated history in Texas, there's now a renewed push to have more teens receive the human papillomavirus vaccine.

HPV is a group of sexually transmitted viruses that can cause cancer in the cervix, mouth and throat, anus, penis, vulva and vagina. The Centers for Disease Control and Prevention estimate that about 80 million people currently are infected with a strain of HPV, and there are 14 million new cases a year.

The vaccine is recommended now for all boys and girls at either age 11 or age 12, but you can give it as early as 9 and as late as 26 for women and 21 for men. When the vaccine first came out, it was recommended as a three-dose series, but in 2016, the Centers for Disease Control and Prevention switched to two doses six months to 12 months apart for kids 9-14. Older than 15, the CDC still recommends three doses: the first one is a month or two apart from the first dose, and the third is six months apart from that dose. The key is trying to get the vaccine administered before a child becomes sexually active.

Now, 13 years after the first HPV vaccines came on the market, the CDC estimates that in 2017 about 65.5 percent of teens ages 13-17 nationally had at least one dose of the vaccine, and 48.6 percent were up to date with their HPV vaccines, receiving either two or three doses depending on their age. In Texas, only about 57.8 percent of teens were vaccinated for it in 2017, and 39.7 percent were up to date, according to the latest numbers.

This same study compared other vaccines for teens. The rates of vaccination nationally were much higher for measles, mumps, rubella at 92.1 percent nationally and 84.7 percent in Texas; and tetanus, diphtheria and pertussis at 88.7 percent nationally and 83.2 percent in Texas.

So, what's stopping us from giving our teens a vaccine that could prevent cancer?

Erin Johnson, pediatric nurse practitioner with Texas Children's Pediatrics in Austin, says the conversation she has with parents around this vaccine compared with others is that "HPV tends to be more touchy. You are dealing with a sexually transmitted disease."

For parents, it's looking at your 11- or 12-year-old and thinking that they might one day have sex.

Doctors also didn't have a lot of in-the-field U.S.-based research into the vaccine's effectiveness. Instead they cited reductions in HPV and future cancer rates in places like Australia, which had a more robust HPV vaccination program.

A new study from Ohio was published in the February issue of Pediatrics by the American Academy of Pediatrics. That study from 2006 to 2017 tested more than 1,500 women ages 13 to 26 for HPV. These were women who had been given the vaccine and those who had not. Researchers studied the initial vaccine, which covered four strains of HPV; a 2009 version, which covered two additional strains; and the new vaccine, which covers nine strains and was released in 2016.

The studies found that not only did the researchers see a reduction in HPV strains that were targeted by the vaccine in vaccinated women, they also saw a reduction in HPV strains in unvaccinated women. Though not always consistent, the researchers believe that they are seeing herd protection — the idea that as more people are vaccinated, the unvaccinated also get protection as there are fewer people to spread the virus. Herd immunity is what we saw in diseases like smallpox and, until recently, measles and mumps. (As more people have decided not to vaccinate, more measles and mumps cases have increased as herd immunity diminished.)

The researchers also studied women in four different waves. The later the wave, the more HPV cases decreased. For the women who were vaccinated with the nine-strain vaccine, they saw a decrease in HPV from 46.6 percent in wave 1 to 13.5 percent in wave 4. Those who were vaccinated with a four-strain vaccine decreased from 35.0 percent to 6.7 percent. Those who had the five-strain vaccine saw a decrease from 23.4 percent to 7.3 percent.

The unvaccinated women saw a decline of 43.4 percent to 42.1 percent in the nine-strain and a decline of 32.4 percent to 19.4 percent in the four-strain type. The five-strain type saw an increase of 22.9 percent to 36.1 percent.

More importantly, the vaccine was 71.7 percent effective in wave 2, 90.6 percent in wave 3 and 80.1 percent in wave 4.

Johnson says she doesn't see a lot of reactions to the vaccine, but they are normal reactions that can happen with any vaccine such as soreness, redness and swelling. They also watch for a fever above 102 or a rash.

HPV, she says, "is a silent disease."

"Cervical cancer takes years, if not decades, to develop," Johnson says. "This is protecting them for 10-plus years in the future when the highest incidents of cancer occur."