Does HPV vaccination increase cancer risk in carriers?
August 28, 2013 7:42 AM   Subscribe

People who are already carrier of HPV 16 or 18 viruses increase their cancer risk by 44.6% by getting vaccinated. Or so anti-vaccination activists claim. Can anyone judge if this claim is true?

They refer to this document: I do find the number "44.6" in that file, but I'm unsure what to conclude from it. I'm a 40-something male who wants to protect himself and future partners. I have a limited sexual history but will likely soon sleep with ladies who have multiple partners. In my country vaccines are cheap. I am concerned about side effects.
posted by anonymous to Health & Fitness (4 answers total) 4 users marked this as a favorite
The "44.6%" seems to refer to the reduction in efficacy in preventing cervical cancer people who aren't just carriers, but are both seropositive and PCR-positive - they have an active infection that they haven't cleared. They then go on to comment that people with active ongoing infections have a higher risk of cervical cancer to begin with, compared to people who have never been exposed, or who were exposed and are now cleared/dormant. So they can't necessarily attribute the increase in cervical cancer in that subgroup purely to Gardasil. They can say that Gardasil doesn't work as well in preventing cervical cancer in those specific people, though. The subgroup in question was about 6% of the test group.

The relevant quotations:

There were two important concerns that were identified during the course of the efficacy review of this BLA. One was the potential for Gardasil™ to enhance disease among a subgroup of subjects who had evidence of persistent infection with vaccine-relevant HPV types at baseline. The other concern was the observations of CIN 2/3 or worse cases due to HPV types not contained in the vaccine. These cases of disease due to other HPV types have the potential to counter the efficacy results of Gardasil™ for the HPV types contained in the vaccine.

Therefore, while the subgroup from study 013 remains a concern of the clinical review team, there is some evidence that this represented an unbalanced subgroup where Gardasil™ recipients at baseline had more risk factors for development of CIN 2/3 or worse. Furthermore, when the subgroups from three studies are combined, these groups appear to be more similar. Finally, there is compelling evidence that the vaccine lacks therapeutic efficacy among women who have had prior exposure to HPV and have not cleared previous infection (PCR positive and seropositive), which represented approximately 6% of the overall study populations.

posted by vetala at 7:59 AM on August 28, 2013 [1 favorite]

The authors of that document explain that although one study found the 44.6% increased cancer risk, the study methods were flawed and the gardasil vs. placebo groups had inherent differences that were likely to cause the differences in cancer observed (ex: PAP results, smoking, and previous STD infections were all higher in the gardasil group before treatment). They then listed additional studies with much higher sample sizes that didn't show an increased risk in the gardasil group.

"This demonstrated a limitation of the evaluation of small subgroups, where subgroups might have imbalances in baseline demographic characteristics. In this case, it appeared that subjects in this subgroup of study 013 who received Gardasil™ might have had enhanced risk factors for development of CIN 2/3 or worse compared to placebo recipients." (p14)

Even without doing additional research, it seems like the anti-vaccine people are "creatively interpreting" the document they cite, which is probably the most "convincing" one they could find. Given that, I wouldn't be worried at all. (And I'm really not - I plan to get the gardasil vaccine soon and I am female and a cancer researcher, if that helps).
posted by randomnity at 8:02 AM on August 28, 2013 [8 favorites]

I'll also add that even if there were real evidence that gardasil vaccination increases cervical cancer in HPV carriers (which there isn't), you still have nothing to worry about if you don't have a cervix (like most men).
posted by randomnity at 8:20 AM on August 28, 2013 [3 favorites]

And of course, a relevant XKCD. (Link to forum)

The anti-vaxxers cherry picked a very small, unique set of people who already have higher risks and drew conclusions that are, practically speaking, without merit. It may be the case that under even more extraordinary circumstances, the risk is even doubled...or quintupled! You just have to exclude people who don't get cancer from your sample population. Voila!
posted by Xoebe at 2:20 PM on August 28, 2013

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