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HPV Vaccine May Only Require Two Doses

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Gardasil and Cervarix, the two vaccines available to help prevent precancerous and cancerous lesions caused by the human papillomavirus (HPV) may only require two injections instead of three, according to researchers in Costa Rica.

In studying over 7,000 women in Costa Rica, where the majority of clinical testing was done, a review of the data shows that two injections were as good as three in providing immunity. While one injection was also just as good, there were too few participants and events occurring in this population but the overall effectiveness was 80 percent regardless of the number of shots given.

While this information was also confirmed by the NIH (National Institutes of Health) they stated that more research would be needed to determine if the lesser number of doses would provide as much long-term protection as it currently does.

Having three doses for the vaccine may make compliance an issue and be what accounts for the declining number of women receiving the vaccine. From 2009 to 2010 the increase in the number of women completing the series increased only 5.2 percent bringing the total to 32 percent.

This information was the unintended result of those enrolled in the Costa Rica study to actually complete the three dose series as a result of pregnancy or other reasons. In other words, the study called for three doses but other issues prevented that from happening.

When researchers then reviewed the data four years later, they found that those who had received only two doses had the same degree of immunity as those who received the three shot series.

NCI epidemiologist Aimee R. Kreimer, PhD, stated that at least a decade of follow-up will be needed to determine if the women who got less than the full series will remain as fully protected as those who got all three doses of the HPV 16/18 vaccine. Until then, it is not likely that the three dose recommendation in the U.S. will change.


HPV Vaccine: Two Doses as Good as Three? Physician's First Watch. N.p., n.d. Web. 14 Sept. 2011.

Human Papillomavirus (HPV) Vaccines - National Cancer Institute.

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