The April 18, 2013 edition of the British Medical Journal contained the results of Australia’s new campaign to vaccinate young women against the Human Papillomavirus (HPV), associated with genital warts and an increased incidence of cervical cancer. This news was brought to my attention by a Slate article by Phil Plait discussing the politics of vaccination and how they get particularly how when the vaccine in question is against a STD. I suggest you read that article if you have any interest in exploring that hot-button topic and how it goes head-to-head-against an abstinence-only policy.
Although those questions intrigue me, I simply want to point out the data behind HPV and how the new vaccines are dramatically effective. First, I think it’s important to examine just who has HPV.
According to the CDC’s report on HPV, approximately 79,000,000+ people in the USA have HPV. That’s a pretty high number given that the Jul 2011 US census reported that the US population is only 311,591,917 – and about 70 million of those people are under 17, the average age the Kinsey Institute reports that kids lose their virginity. Let’s call it half of Americans who have had sex, also have HPV – this estimate agrees with the CDC’s data on HPV.
There are a number of different HPV viruses and some of them are more dangerous than others. Of the ~40 strains of HPV, two of them (6 and 11) are responsible for most genital warts, but are not associated with cancer, whereas two different strains (16 and 18) are linked to the majority of cervical cancer cases. Gardasil, a quadrivalent vaccine made by Merck, protects against all four of these strains, while Cervarix is a bivalent vaccine made by GlaxoSmithKline and protects against strains 16 and 18.
In 2007, Australia began offering free vaccinations against HPV for girls 12-13 years old. Fortunately, the vaccine being offered was the Merck vaccine, so the efficacy of the vaccine could be readily tracked by using genital warts as an indicator rather than having to wait to measure cervical cancer rates at a much later time point. The caveat is that this trial assumes that the reduction in genital warts accurately models an expected reduction in cervical cancer, despite the two conditions resulting from different strains of the virus. I’m comfortable with this assumption, but I do think that caveat needs to be kept in mind.
So, what are the results? It’s been five years. According to estimates from the US population, these girls should be starting to have sex now. Are they getting genital warts?
“In the vaccination period, the proportion declined dramatically by 92.6%, to 0.85% in 2011”
Further, not only are fewer vaccinated girls developing genital warts, but it looks like the vaccination campaign in also benefiting unvaccinated girls as well (although this is an assumption about causality on my part).
Remember, not ALL genital warts are caused by the four strains in the vaccine – and, these vaccines will only work on people who have not caught HPV already.
Altogether, this looks to be a whoppingly successful campaign – one that the US should strongly consider mimicking.