written by Tara Haelle

Two different studies related to the HPV vaccine were published recently which, together, are somewhat concerning. One study concerned the vaccine’s effectiveness. The other dealt with how many parents are opting not to give their daughters the vaccine – and the reasons why.

Let’s review the more recent one first, published in Pediatrics yesterday, that found increasing percentages of parents are actually deciding not to vaccinate their teenage daughters against HPV.

Recall first that HPV stands for human papillomavirus, a sexually transmitted disease that includes over 100 different strains. Most of these strains are effectively harmless and go away on their own, but several can cause genital warts and cervical cancer. HPV is also linked to a couple other cancers, such as anal cancer and throat and mouth cancer. The HPV vaccine used in the US, Gardasil, protects against four strains: HPV-6 and 11, which are responsible for about 90 percent of all genital warts, and HPV-16 and 18, which are responsible for about 70 percent of all cervical cancers.

The CDC recommends that girls be routinely given the HPV vaccine at 11 and 12 years old. Those aged 13 to 26 who haven’t gotten the vaccine yet should also get it, though it will only protect them against any strains of HPV they have not already contracted. (HPV is incredibly common – about 6.2 million people contract it each year.)

The good news in the new Pediatrics study is twofold: results from three National Immunization Surveys of Teens from 2008 through 2010 reveal that more doctors are advising parents to get their daughters the shots, and more parents are doing so. In 2008, 46.8 percent of clinicians were recommending the vaccine, which increased to 54.5 percent in 2009 and 52.4 percent in 2010. In 2008, 83.8 percent of adolescent girls were not up to date on their HPV shots, which dropped to 76.2 percent in 2009 and 75.2 percent in 2010.

Still, though, that’s three quarters of US girls who are not protected against the only cancer we actually have a vaccine for. And the more concerning news is that alongside the slowly increasing HPV vaccination rates is a disturbingly rapid increase of parents saying they won’t give their daughter the vaccine because of safety concerns or side effects.

Overall, the percentage of parents who don’t intend to vaccinate their daughters increased from 39.8 percent in 2008 to 43.9 percent in 2010. Among the reasons given were that the vaccine was “not recommended” (which it is), it was “not needed” (which it is if you don’t want your daughter to be at risk for cancer), “lack of knowledge,” and that their daughter was “not sexually active” (that’s the point – you’re supposed to give the vaccine well before a girl becomes sexually active, and past studies have shown that giving girls the vaccine has no impact on when they decide to start having sex).

But the big jump was in parents who said they didn’t plan to vaccinate their daughters because of safety concerns and/or side effects: from 4.5 percent in 2008 to 7.7 percent in 2009 to 16.4 percent in 2010. That’s nearly a fourfold increase. In fact, in 2010, safety concerns were the second most cited reason, behind “not needed or not necessary” at 17.4 percent. The reasons given for teens who were not up to date on their DTaP (diphtheria-tetanus-pertussis/whooping cough) or MCV4 (meningitis) vaccines did not include a similar increase related to safety concerns.

Yet here’s the thing: there are no serious side effects to the HPV vaccine. It’s actually one of the safest vaccines that exists. There are serious side effects, though extremely rare, to various other vaccines. For example, a recent study found there’s good evidence that an additional 1.6 out of every one million people vaccinated against the 2009 H1N1 vaccine likely developed Guillain-Baire syndrome, a nerve disorder, from the shot.

But the only confirmed side effects from Gardasil among the 46 million girls who have received it in the US are the standard ones associated with many vaccines and medications: headache, nausea, fever, vomiting, fainting, dizziness and pain, swelling, itching, bruising or redness at the injection site. Among these, the injection site reaction and headache or nausea are the most common.

In theory, it is possible to have an allergic reaction to a component in Gardasil, as is possible with any vaccine or medication. However, none has been confirmed to have happened so far. Early reports of blood clots that people feared were caused by Gardasil were found to be unrelated to the vaccine: 90 percent of those who had a blood clot after the vaccine already had a risk factor for blood clots, such as obesity, smoking or taking birth control pills.

The increase in safety concerns among parents shows that the message about the HPV vaccine’s safety record is clearly not getting out, and apparently, misinformation about side effects not actually caused by Gardasil are frightening parents. The other message not getting out is that this vaccine is recommended and that girls should get it long before they become sexually active.

And that brings us to the study that came out last week in the Journal of the National Cancer Institute, providing more evidence of just how effective the vaccine is. Researchers investigated the medical records of 124,000 girls and women, aged 10 to 44, who had received the HPV vaccine between 2006 and 2010. It is too soon to assess decreases in cervical cancer rates among vaccinated populations – though we are pretty much certain to see this in the coming years – so the researchers were looking at the rates of genital warts in vaccinated females as compared to over 2 million other women and girls who were not vaccinated.

The researchers determined that the vaccine was a whopping 93 percent effective in preventing genital warts among girls who were vaccinated before age 14. That means genital warts declined 93 percent among these girls compared to those not vaccinated before age 14. If they were vaccinated between 14 to 16 years old, the effectiveness against genital warts was 80 percent. If girls receiving three doses had gotten the first shot before age 20, the effectiveness was 76 percent. For those vaccinated between 20 and 22 years old, the effectiveness was only 48 percent. After age 22, the researchers could not detect any significant level of effectiveness.

In other words, the study clearly showed that the earlier girls are vaccinated, the more likely they are to avoid contracting genital warts. It stands to reason that similar trends will be seen with cervical cancer in a decade or two.

These high rates of effectiveness in younger girls are great news, but they are also the reason I find it so disturbing that more parents are becoming concerned about the HPV vaccine’s safety and not vaccinating their girls because of it. The HPV vaccine literally saves lives. It is also the only vaccine that exists which actually prevents a cancer. Over 12,000 women were diagnosed with cervical cancer in 2009, and 3,900 women died from it that year. Somehow, the message about this vaccine’s safety and effectiveness needs to get through to parents and teens.

Funding Note: the study on HPV effectiveness was funded through a research grant from the pharmaceutical company Merck Sharp & Dome Corp, which manufactures the HPV vaccine, and the study on teen vaccination rates was funded by the US Department of Health and Human Services.