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HPV Vaccines: Do I Need All Three Doses?

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HPV vaccines involve getting three shots over six months, but what can you tell us about the recent news that only one dose of an HPV vaccine might actually be effective in protecting against cervical cancer?

When someone is infected with HPV, their immune system kicks in and creates an antibody response to the virus. The way the two HPV vaccines currently on the market work, of course, is by causing the body to create this antibody response without actually infecting those getting the shots with HPV. They trick the immune system into thinking HPV is present.

The vaccines actually cause an antibody response that’s much, much higher than what you see with natural infection.

This buzz is being spurred by research (Safaeian et al., Cancer Prev Res 2013) done with women who were part of large vaccine trials with Cervarix®, GlaxoSmithKline’s vaccine that covers the two HPV types found in about 70% of cervical cancers worldwide. While the study was designed to give women all three doses, for a variety of reasons (people drop out, miss follow-ups, become pregnant, etc.) a number of subjects received fewer than the intended number of shots.

So, the investigators running this study inadvertently ended up with a pool of women who received one, two, or three of the shots. This allowed for comparison of antibody levels in each group, not only to each other BUT also to women who have HPV and have an antibody response generated solely by natural infection.

They found that regardless of how many shots the women had, they still had a detectable antibody response that 1) was higher than what women with HPV develop on their own and 2) that lasted for at least four years.

The antibody response among those receiving two- or three-doses was similar, no significant difference at all. The response in those who only had one dose was lower than those receiving two- or  three-doses, but was still higher (and sustained) compared to antibody levels found in women who had HPV and had not received the vaccine.

This naturally raises the question as to whether or not fewer than three doses of an HPV vaccine will perhaps convey protection against the virus and cervical cancer. We don’t know for sure yet that it will, but this research is compelling. At this point, no changes are being made to the recommendation for three doses spaced over six months. Also keep in mind this study was done only with the GSK vaccine, not Merck’s Gardasil® vaccine that’s also commonly used around the world.

But who knows, if more studies also demonstrate value with fewer doses of the vaccines we may eventually see an alternative two-dose regimen available. In the meantime, those being vaccinated should still receive all three shots (and vaccinated women need to continue regular cervical cancer screening).

--The HPV Resource Center Staff


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