Thursday, February 01, 2007

Herd Immunity

I saw this conversation at feministing about the CDC's recommendation to add the HPV vaccine Gardasil to the regimen of immunizations required for children enterting public schools, and it turned out to be part of a happy coincidence. It just so happens that a lot of the questions being asked in the thread were addressed in a study in a copy of Emerging Infectious Diseases that I picked up today. (The happiest part of the coincidence? It gives me a chance to brag. The cover paper in the issue is something to which I actually contributed a minor amount of elbow grease. It's like I'm a real scientist, kind of!)

The paper, entitled Model for Assessing Human Papillomavirus Vaccination Strategies, by Elbasha et al, took a statistical look at the possible costs and benefits of different HPV vaccination strategies. The cheif concern is preventing HPV-associated cervical cancer, though check out this first sentence:
Human papillomavirus (HPV) causes cervical intraepithelial neoplasia (CIN); cervical, anal, penile, vaginal, vulvar, and head/neck cancers; anogenital warts; and recurrent respiratory papillomatoses, resulting in disease and death in both women and men (1).
So, worry not wingnuts: we're not just trying to save women's lives here.

Feministing commenters wondered why boys and men aren't recommended to be vaccinated. See the paper's abstract:
We present a transmission dynamic model that can assess the epidemiologic consequences and cost-effectiveness of alternative strategies of administering a prophylactic quadrivalent (types 6/11/16/18) human papillomavirus (HPV) vaccine in a setting of organized cervical cancer screening in the United States. Compared with current practice, vaccinating girls before the age of 12 years would reduce the incidence of genital warts (83%) and cervical cancer (78%) due to HPV 6/11/16/18. The incremental cost-effectiveness ratio (ICER) of augmenting this strategy with a temporary catch-up program for 12- to 24-year-olds was US $4,666 per quality-adjusted life year (QALY) gained. Relative to other commonly accepted healthcare programs, vaccinating girls and women appears cost-effective. Including men and boys in the program was the most effective strategy, reducing the incidence of genital warts, cervical intraepithelial neoplasia, and cervical cancer by 97%, 91%, and 91%, respectively. The ICER of this strategy was $45,056 per QALY.
By their metrics, every quality-adjusted year added to each American's life by ppting for the strategy of vaccinating both males and females would cost almost ten times as much as the less-effective-against-disease strategy of vaccinating girls 12 and under with a "catch-up" program for females up to the age of 24. This only augments the case that Ann lays out in her TAPPED piece about the opportunity for public health that Gardasil presents; there's much to be gained, but there's also much to be spent. Elbasha et. al. use the amount of $360 per vaccination regimen in their calculations, an amount that would be difficult to come up with on a less-than-living wage job. With excessive pork-barrel spending adding up by the second in Washington, public health officials would be irresponsible not to take the relative bargain in the female-only vaccination strategy.

A 78% reduction in cases of cervical cancer would mean 2886 fewer deaths in the United States per year (according to these stats).

UPDATE: More conversation about Gardasil inspired me to write another post about other issues people are debating. See it here.
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