The NIH announced results of a study that found that “two doses of the human papillomavirus (HPV) vaccine Cervarix were as effective as the current standard three-dose regimen after four years of follow-up.” The results of the study, based on data from a community-based clinical trial of Cervarix in Costa Rica, appeared online Sept. 9, 2011, in the Journal of the National Cancer Institute. NIH said the NCI-sponsored Costa Rica Vaccine Trial was designed to assess the efficacy of Cervarix in a community-based setting. Women ages 18 to 25 years were randomly assigned to receive the HPV vaccine or a Hepatitis A vaccine as the control treatment. Although the investigators intended to administer all three doses of the assigned vaccine to all 7,466 women in the study, about 20 percent of the participants received only one or two doses of the HPV or control vaccine. A third of women did not complete the vaccine series because they became pregnant or were found to have possible cervical abnormalities, reasons that would not likely bias the findings.
NIH said that the investigators found that, “after four years of follow up, two doses of the vaccine conferred the same strong protection against persistent infection with HPV 16 and 18 as did the full three-dose regimen. From just a single dose, they also observed a high level of protection, but they are cautious about the long-term efficacy of a single dose because other vaccines of this type usually require a booster dose. Additional studies are needed to evaluate the efficacy of a single dose, as well as the duration of protection for both one and two doses.” Aimée R. Kreimer, Ph.D., lead author and investigator in NCI’s Division of Cancer Epidemiology and Genetics, commented, “Our study provides evidence that an HPV vaccine program using two doses will work. It may be that vaccinating more women, with fewer doses for each, will reduce cervical cancer incidence more than a standard three-dose program that vaccinates fewer women. The main question will be whether the duration of protection from fewer doses is adequate.”
vaccines and global health :: ethics and policy 