Tuesday, February 8, 2011

Dodge This Bullet...HPV

Yesterday I mentioned that the New England Journal of Medicine recently published a study regarding HPV vaccine efficacy in boys. Today I'd like to explain the study. The title is "Efficacy of Quadrivalent HPV Vaccine against HPV Infection and Disease in Males". "Quadrivalent" refers to the fact that the vaccine targets four strains of the Human Papilloma Virus: strains 6 & 11, that cause 90% of genital warts, and strains 16 & 18, which cause the majority of cervical cancers (roughly 70%).
I'll start by saying that yes, the study was partially funded by Merck, the manufacturer of the vaccine. That being said, I do not feel it negates the study, although obviously it introduces some bias. They took over 4000 boys/young men age 16-26, from 18 countries, and gave half a placebo vaccine series, and half real. The study was double blind (no one knew what they were giving or getting), and randomized (which raises the quality of the study.) Some of the participants were fully screened initially to determine if they already HAD any HPV strains, and others were not. Note that in "real life medicine", we have no way to test people ahead of time to see if they have already contracted HPV.

In the young men with unknown prior HPV status, the vaccine had an efficacy of 60%. In those known to be HPV negative initially, the efficacy was 90%. It is not surprising that the vaccine would appear to work better in those that did not already have some strain of HPV, and this supports the reasons to vaccinate youth BEFORE they are sexually active. I thought it was interesting that they ended up with 1% of the placebo subjects developing genital warts- the same as in the general population. I am encouraged that the incidence in those vaccinated dropped to 0.1%.

The devil is always in the details, and how people pull out statistics. I could note, for example, that 3 patients in the placebo group received gun shot wounds, while only one in the vaccine group did- but obviously the vaccine did not prevent gun shot wounds! The good news here is that true adverse events were minimal and of uncertain relationship to the vaccine.

BOTTOM LINE: HPV vaccination can significantly reduce the incidence of genital warts in young men as well as young ladies, with minimal side effects.

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