A new study has recently found that it may be possible to vaccinate women with only one dose of the human papillomavirus (HPV) vaccine instead of three, with the single dose generating long-term immune response and protection against new HPV infections.
Researchers at the National Cancer Institute (NCI) have found that one dose of HPV 16/18 L1 VLP vaccine (Cervarix®, GlaxoSmithKline, Research Triangle Park, NC) produced antibodies against the viruses that remained stable 4 years after vaccination.1 These findings challenge previous medical dogma that protein subunit vaccines require multiple doses to generate long-lived responses, according to study investigator Mahboobeh Safaeian, PhD, who is with the Division of Cancer Epidemiology and Genetics at the NCI in Bethesda, MD. “It was not known if this protection coincided with sustained antibody levels,” Dr. Safaeian told ChemotherapyAdvisor.com.
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New Data Supports Simplified Vaccine Schedule
The data for this current study came from a phase 2 clinical trial testing the efficacy of Cervarix in women in Costa Rica. Serum antibody levels from 78 women (single-dose group), 192 women (two-doses group), and 120 women (three-doses group) were compared with the results of data from 113 women who did not receive vaccination but had antibodies against the virus due to previous HPV infections. The study showed that 100% of the women in all three groups had antibodies against HPV 16 and HPV 18 at 4 years postvaccination. The researchers found that, although the antibody levels among women who received one dose were lower than those women who received the full three doses, the levels appeared stable. In addition, the levels of antibodies in women from the single-dose group and two-doses group were significantly higher than the levels of antibodies in women who did not receive vaccination but had prior HPV infection.
Dr. Safaeian indicated these new study findings suggest a simplified vaccine schedule might be cheaper, simpler, and more likely to be implemented around the world. In addition, she noted that, in some parts of the world, only two doses of HPV vaccine are now recommended, including Chile and British Columbia, Canada. However, she explained, additional studies are warranted before policy guidelines can be changed.
This study did not look at the quadrivalent HPV vaccine (Gardasil®, Merck & Co., Inc., Whitehouse Station, NJ), which is more widely used in the United States and in many other countries. L. Stewart Massad, MD, a gynecologic oncologist at the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine, St. Louis, MO, said that this study is exploratory and generates an interesting hypothesis, but needs correlation with clinical end points. “There is nothing in here that says a single dose will reduce HPV infections or cut the risk of cervical cancer or cancer precursors like CIN3,” Dr. Massad told ChemotherapyAdvisor.com.
The study suggests that it is possible that a single dose may be efficacious, and would thus make completing vaccination much simpler. However, Massad noted that many eligible women and girls still don’t get their first dose. “It’s too early to speculate about whether a single dose would lower cervical cancer rates. It’s a very promising study by our National Institutes of Health in collaboration with the Costa Ricans, and was well designed; we will need to wait to see if it leads to [data] that show a change in cervical end points,” said Dr. Massad.
Jane Dimer, MD, Women’s Health Service Line Chief and Maternity Child Clinical Service Chief for the Group Health Cooperative, in Seattle, WA, also thinks these vaccine findings are very important and may lead to new prevention and treatment strategies for cervical cancer. “All of the screening and treatment strategies with regard to HPV-related disease have now changed quite a bit from a historical scenario where Paps [pap smears] were used as a screening strategy for cervical cancer and the individual results were triaged one-by-one,” Dr. Dimer told ChemotherapyAdvisor.com. “Now, however, the screening and treatment strategy has changed to looking at the whole picture of the patient, not only the Pap test result, but also her HPV status, immune system status, and other medical risks as well.”
According to Dr. Dimer said that, currently, approximately 30% of young women are immunized with the HPV vaccine in the United States. She explained that in order to have a population-wide decrease in the overall risk of HPV-related disease like cervical cancer, vaccination rates need to be 90% or higher in girls, or at least 50% of boys and 50% of girls need to be immunized. Furthermore, this study may help lead the way to a better understanding of etiology of some cervical cancers and point to improved therapies. “Clinical oncologists are increasingly aware that the more we learn about the basic biology and etiology of cancer, the more we can hope that other types of targeted anticancer vaccines can be on the horizon soon,” concluded Dr. Dimer.
Reference
- Safaeian M, Porras C, Pan Y, et al. Durable antibody responses following one dose of the bivalent human papillomavirus L1 virus-like particle vaccine in the Costa Rica Vaccine Trial. Cancer Prev Res (Phila). 2013;6(11):1242-125050.
