Fewer doses of HPV vaccine may confer necessary long-term protection against new infection

NCI scientists report that two doses of a human papillomavirus (HPV) vaccine, trademarked as Cervarix, resulted in similar serum antibody levels against two of the most carcinogenic types of HPV (16 and 18), compared to a standard three dose regimen. Among women who received only one dose, antibody levels were also high and remained stable four years after vaccination. The results suggest that fewer doses of an HPV vaccine may confer necessary long-term protection against new infection and appeared Nov. 4, 2013, in Cancer Prevention Research.

Mahboobeh Safaeian, Ph.D., an investigator in the Division of Cancer Epidemiology and Genetics at NCI, and her colleagues, measured HPV antibody levels in women enrolled in the NCI Costa Rica Vaccine Trial. Previously, data from this trial demonstrated vaccine efficacy against new persistent HPV16/18 infections, for two vaccine doses (see http://www.cancer.gov/newscenter/newsfromnci/2011/HPVvaxDosing) which was comparable to a standard three doses. In this latest study, investigators compared the level and duration of antibody response in three groups of women vaccinated with one, two or three doses of Cervarix. They also measured immune responses of unvaccinated women who, at enrollment, were found to have existing antibody levels, presumably from past HPV infection. Women who received just one dose had lower antibody levels against HPV 16/18, compared to women who received all three doses, and their levels remained stable from six to 48 months after vaccination. If these findings are confirmed by other studies, they would potentially affect cost and logistics of vaccination programs in low-resource settings, where more than 85 percent of cervical cancers—the most common cause of cancer death in these women—occur.