HPV vaccine protection lasts more than 6 years

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The human papillomavirus (HPV) vaccine Cervarix, produced by GlaxoSmithKline, offers protection against the two major cancer-causing strains of HPV, (HPV-16 and HPV-18) for more than 6 years, according to research published online today in the British medical journal the Lancet. The analysis, led by Dr. Cosette Wheeler from the University of New Mexico, included more than 1,000 women between the ages of 15 and 25, who had normal cervical cells and no evidence of HPV infection at the study’s onset. Roughly half of the women were given the Cervarix vaccine, and half given a placebo. Ultimately 700 women across three nations completed the study, which included HPV screenings every six months for up to 6.4 years. At the end of the study period the researchers found that, not only did the vaccine protect against HPV-16 and HPV-18 for the full duration of the follow-up, but it also protected against HPV-31 and HPV-45, two additional strains of the virus that are responsible for 10% of cervical cancer cases.

Vaccine efficacy against short-term HPV-16 and HPV-18 infections was 95%, and 100% against longer term infections—persisting for 12 months. (Vaccine efficacy is defined by the drop in disease rate among vaccinated subjects, compared with the disease rate in the placebo group.) Researchers also found that, for those in the study group, the vaccine was 100% effective in protecting against cervical intraepithelial neoplasia (CIN), or the growth of abnormal cells on the cervix that is often a precursor to cervical cancer. The growing occurrence of CIN cases among the placebo group suggests that participants in the study group were also frequently exposed to, but protected from, HPV infections. As the researchers sum up:

“The study population was continuously exposed to HPV infections, as indicated by the continuous accrual of CIN cases in the placebo group, showing that the vaccine confers sustained protection and that efficacy does not wane up to 6.4 years after first vaccination.”

Previous research has shown that the equivalent vaccine, Gardasil, from fellow pharmaceutical giant Merck, protects for up to five years. These current findings add to previous research suggesting that HPV vaccines may offer the long-term protection necessary to prevent the development of cervical cancer later in life; Cervical cancer generally manifests some 30 years after adolescence, researchers point out, meaning that persistent protection is key. Further research is needed to confirm these findings, the researchers say, but these initial results are very promising. As Wheeler and colleagues conclude, future research should yield evidence of even more long-term protection: “[W]e expect protection to continue for many more years.”

Thus far 15 cancer-causing strains of HPV have been identified, though there are more than 100 types of the virus. In the U.S., cervical cancer is second only to breast cancer as a cause of cancer-related deaths among women, and a growing percentage of cervical cancer cases are now found in the developing world. According to researchers, 2002 data suggests that worldwide there are 500,000 new cases of cervical cancer and 270,000 deaths from the disease each year.

Cervarix was approved by the Food and Drug Administration as an HPV vaccine in October of this year.