Is Gardasil More Effective in Older Teens?

Nearly 18 months ago, I spoke to Diane Harper, a gynecologist who conducted some of the clinical trials on Merck's Gardasil vaccine, which protects against the cervical cancer-causing human papillomavirus, or HPV. At that time, I was trying to decide whether to get my own 12-year-old vaccinated; I was worried the vaccine was too new for us to know its full safety profile, and I ultimately decided to delay giving the vaccine to my daughter until she was older.

Harper told me then that the vaccine's efficacy hadn't been tested in anyone under age 16, and she wasn't sure whether it even worked in preteens. On the flip side, she also told me that she frequently administered the vaccine to women in their 30s, 40s, and 50s, for whom the vaccine is not approved. Many of these women were hitting the dating scene again after divorce or widowhood and wanted protection against the sexually transmitted virus.

[See more on older women getting Gardasil.]

I called Harper again last week—she's now a professor of obstetrics and gynecology at the University of Missouri in Kansas City—to find out if she'd heard about the cases of deadly ALS (aka Lou Gehrig's disease) that followed Gardasil vaccination in two teens and possibly a third. She said she knew about them and had even spoken with Phil Tetlock, the father of 15-year-old Jenny, who was vaccinated with Gardasil in 2007 and died two weeks ago from ALS.

"I think there's a strong possibility that Gardasil was the catalyst that set off the ALS," Harper says. "It could have been the straw that broke the camel's back in a child who was already predisposed to the condition." In other words, it's possible Jenny would have eventually developed the disease from another immunological trigger, like a severe stomach virus or a standard flu vaccine, and that the Gardasil shot accelerated the onset of ALS. On the other hand, it's also quite possible that there's no link at all between the Gardasil shot and Jenny's illness.

[See how the CDC is taking a closer look at paralysis cases after vaccinations.]

While Harper firmly believes Gardasil is a valuable vaccine, she says, "I do think it's wrong for physicians to tell parents that it's 100 percent safe." She also has previously spoken publicly about her impression that Merck was too aggressive in marketing the vaccine to preteens and in lobbying state legislators to make Gardasil mandatory for young girls. It's worth noting that Harper, while at Dartmouth, once received grants from Merck to conduct its clinical trials and served on Merck's advisory board, though she has since broken ties with the company.

What's intriguing to me is how much is still unknown about Gardasil. A Merck study published last year shows that a woman's antibody response to the vaccine—which determines its effectiveness—depends in part on whether she has been previously exposed to HPV through sexual contact. In the study, 16-to-26-year-olds who, before they got Gardasil, tested positive for HPV antibodies (an indication that they'd been infected) had a stronger vaccine-induced antibody response to three of the four HPV strains Gardasil protects against compared with those who initially tested negative for HPV.

"It would not be surprising to see better protection against cervical cell abnormalities in those who had previous exposure to HPV before being vaccinated," Harper says, "compared to those who were virgins when they received Gardasil." More information about this will be known in May with the publication of a study using the HPV vaccine Cervarix, which is routinely used in Great Britain but not yet available in the United States.

There's a strong caveat here, though. While most HPV infections clear the body on their own without causing any harm, women who get vaccinated after they engage in intercourse leave open the possibility that they could be infected, during that initial sexual activity, with a cancer-causing HPV strain that their immune system can't fend off.

Even so, Harper says, there are a lot of misconceptions flying around when it comes to Gardasil. "Many women are scared off from getting it because they think it won't work if they've already been sexually active—which is absolutely not the truth. Their antibody response to the vaccine is much higher than a virginal 12-year-old's."

What I'm starting to see is that the decision to vaccinate a child with Gardasil is a very complex one. Parents certainly need to be told about the known risks—including allergic reactions and fainting—and may be justified in using caution if their daughter previously had a bad reaction (like spiked fevers or seizures) to a different vaccine. If motor neuron diseases like ALS run in their family or if their child had a bad reaction after the first of the three Gardasil shots, says Harper, they may also want to think twice about vaccination. (At least until the CDC finishes its investigation, perhaps.) What's more, all parents need to understand that Gardasil protects against the strains that cause about 70 percent of cervical cancers, not all. So vaccinated women still need Pap smears for early detection.

Just as important, though, is information about Gardasil's potentially lifesaving benefits. Harper points out that the two cancer-causing HPV strains that the vaccine protects against can lead to adenocarcinomas, a cancer that's very difficult to detect through Pap smears and cervical biopsies. Because they're hard to screen for, adenocarcinomas, which account for 25 to 30 percent of all cervical cancers, are frequently diagnosed in advanced stages, when they're most life threatening. Interestingly, the other HPV vaccine, Cervarix, protects against the two strains in Gardasil as well as a third cancer-causing strain. These three strains account for 98 percent of adenocarcinomas and about 83 percent of all cervical cancers, says Harper. But Cervarix, unlike Gardasil, doesn't protect against the HPV strains that cause irritating genital warts. Already widely used in Great Britain, Cervarix is expected to be approved in this country by the end of the year.

Bottom line: If you're the parent of a preteen daughter who's not actively dating and you're hesitant about Gardasil, "there's no rush," says Harper. Certainly, it's fine to follow the government's recommended guidelines to get girls vaccinated at the preferred age of 11 or 12. But if you wait and your daughter subsequently becomes sexually active, it still wouldn't be too late to get her immunized. The vaccine might even be more effective at that point.

Next: The difficulties parents face when they suspect their daughters have been injured by Gardasil.