Thursday, August 25, 2011

Gardasil = Girls Gone Wild?


Stick to your guns, Governor Perry!

Four years ago, Texas governor Rick Perry raised a ruckus when he issued an executive order for all sixth-grade girls to undergo mandatory vaccination against the human papilloma virus, the cause of most cervical cancers and genital warts.  It was a strong and surprising move, especially coming from a politician who believes in teaching kids that cavemen coexisted with dinosaurs.  Critics from the right (and a few from the left) railed against the order, claiming it infringed upon parental rights and taught girls that premarital sex was O.K., despite the fact that the order gave parents the right to opt out of vaccination.  The order was overturned by the state legislature, and mandatory HPV vaccination never went through.  Now that he's running for the White House, Perry is apologizing for his earlier decision, stating, "I didn't do my research well enough."  Was he right then, or is he right now?  Well, Governor, how about if I do the research for you?

The landmark trial that got the HPV vaccine approved by the FDA was the "Females United  to Unilaterally Reduce Endo/Ectocervical Disease," Study, with the totally awesome acronym, "FUTURE II," bringing to mind a popular Disney attraction rather than genital warts.  ("Quadrivalent vaccine against human papillomavirus to prevent high-grade cervical lesions.")  Over 12,000 women ages 15 to 26 years were randomized to three doses of the HPV vaccine or placebo.  The vaccine was designed to protect against two HPV strains that cause 70% of cancers, and two other strains that cause the majority of genital warts.  The primary endpoint, which was carefully selected by Merck, maker of the vaccine, was the rate of cervical cancer or precancer caused by the two HPV cancer-causing strains in women who were not previously infected by these strains.  Got it?  Not the overall rate of all cervical cancer or precancer in all the women, but only a subgroup of cancers in a subpopulation.

The vaccine was extremely effective:  in women without prior infection, the vaccine prevented 98% of cancers and precancers caused by the two strains of virus, and almost 100% formed protective antibodies.  But what if you looked at the entire group of 12,000 women, and all forms of cervical cancers and precancers?  It turns out the efficacy was a disappointing 17%.

So why was the overall efficacy of the vaccine so low?  Two reasons:  First, the women who received the vaccine were still unprotected against the strains of HPV that cause the remaining 30% of cervical cancers.  Second, a good number of the women were already infected with the strains in the vaccine, rendering it useless.

So does that mean we shouldn't bother giving this expensive vaccine because of its low overall efficacy?  Actually, the results of the study strongly suggest that we should be giving the vaccine to girls before they become sexually active.  The CDC reported in 2006 that 70% of girls are sexually experienced by the time they are 19, and another study found that 27% of women aged 20-24 test positive for HPV.  If you follow the American Academy of Pediatrics' guidelines and give the vaccine to presumably uninfected 11- to 12-year-old girls, they should experience a 70% reduction in cervical neoplasms.  I suspect that pharmaceutical companies are probably working on adding more strains to the vaccine, to get the efficacy closer to 100%.

What about the argument that the vaccine will lead to a false sense of security, or an increase in early, sexually risky behavior?  Certainly, there are lot of misconceptions about the vaccine -- for example, that it protects against all cervical cancers, or that you can stop getting Pap smears.  The vaccine shouldn't be given without a fairly sophisticated discussion of the expected benefits.  Presumably, the discussion would be between the parent and the pediatrician, and then ideally, between the parent and the child.  I suspect that a big reason why some parents are reluctant to vaccinate their kids is that they want to avoid an uncomfortable conversation.

As for whether an STD vaccine would be, as one author put it, "a passport to promiscuity," there is very little data.  Four Scandinavian countries recently surveyed 65,000 women about their sexual behavior prior to the introduction of the HPV vaccine.   (Interviewing Swedish supermodels about their sexual proclivities: obviously the brainchild of some repressed male researcher!) They plan on re-surveying them after the vaccination campaign, to see whether it affects their behavior. ("Women's sexual behavior.  Population-based study among 65,000 women from four Nordic countries before introduction of human papillomavirus vaccination.")  HIV vaccine trials have not found an increase in sexually risky behavior among its participants, though many of them were high risk to begin with.  And one survey of adolescent girls found that only about 10% thought that getting the vaccine meant that they were old enough to start having sex.  ("Adolescents' beliefs about their parents' human papillomavirus vaccination decisions.") Frankly, I think most teenagers and young adults are more frightened at the prospect of pregnancy and HIV than they are of HPV, and I doubt the vaccine will do much to alter their behavior.

So should the vaccine should be mandatory in girls?  I say yes, as long as parents have the option to decline.  Making it mandatory would remove its stigma as "the STD vaccine," and countries that have instituted school-based HPV vaccination programs have much higher rates of immunization that those that haven't.  Remember that this wouldn't be the first mandatory vaccine for a sexually transmitted disease; the hepatitis B vaccine is required for elementary school enrollment in most states. 

I do understand the argument that it shouldn't be as compulsory as, say, the measles vaccine, since your child can't catch HPV just by sitting next to an infected person in class.  But if we wait until girls are old enough to consent to the vaccine themselves, it may be too late.  I've seen too many 30-year-olds die agonizing deaths from cervical cancer to let my daughter suffer such a fate.  Even more women have to deal with the infertility resulting from treatment of their cancer or precancerous lesions.  We parents do all that we can to instill our own values into our children, but at a certain point, we have to accept that they will make their own decisions, good or bad.

So man up, Governor Perry!  Apologize for your apology, do the right thing, and become the public health advocate every presidential candidate should be.

Next week:  The HPV vaccine for boys

3 comments:

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