UBC researchers have found that girls who received two doses of the human papillomavirus (HPV) vaccine had immune responses to HPV-16 and HPV-18 infection that were not worse than the responses for young women who received three doses.
HPV infections cause nearly all cases of cervical cancer, which is the second most commonly diagnosed cancer in women worldwide. The study, published in the May 1 issue of JAMA, lends more plausibility to adopting reduced-dose schedules for the vaccine, which would lower barriers to global implementation.
Lead co-investigator Simon Dobson, a Clinical Associate Professor in the Department of Pediatrics and Clinical investigator at the Child & Family Research Institute, noted that more data on the duration of protection are needed before reduced-dose schedules can be recommended.
“Globally, cervical cancer is the second most common cause of cancer morbidity and mortality in women. Human papillomavirus infection has been identified as a necessary cause for the development of cervical cancer, with HPV genotypes 16 and 18 accounting for approximately 70 percent of cervical cancer cases,” according to background information in the article. “Global use of HPV vaccines to prevent cervical cancer is impeded by cost. A 2-dose schedule for girls may be possible.”
Dr. Dobson and colleagues conducted a study to determine whether average antibody levels to HPV-16 and HPV-18 among girls receiving 2 doses were not worse than levels in women receiving three doses. The authors also looked at antibody levels to HPV-6 and HPV-11, and compared girls given two or three doses.
The randomized, phase 3, multicenter study included 830 Canadian females from August 2007 through February 2011. Follow-up blood samples were provided by 675 participants (81 percent). Antibody levels were measured at 0, 7, 18, 24, and 36 months.
The authors write that these are the first data, to their knowledge, “on the duration of the immune response of young adolescent girls to a reduced-dose schedule of quadrivalent HPV vaccine out to three years.” However, “The clinically meaningful difference between the 2- and 3-dose schedules cannot yet be determined.”
“Reducing the number of doses affects vaccine and administration costs as well as potentially improving uptake rates. Evidence-based decision-making in public health has led to reduced-dose schedules for hepatitis B, pneumococcal, and meningococcal serogroup C vaccine programs. There is a balance to be found between the incremental value of an additional dose on population effectiveness and the opportunity costs of using the resources required for the extra dose in other public health programs. This is especially the case for HPV vaccines at their present cost.”