A National Cancer Institute (NCI) study has found that women vaccinated with a single dose of a human papillomavirus (HPV) vaccine had antibodies that remained stable in their blood for 4 years. As a result, investigators conclude that a single dose of the vaccine may be enough to generate a long-term immune response against HPV infections and cervical cancer.
The research evaluated whether 2 doses, or even 1, of the HPV type 16/18 L1 virus-like particle vaccine (Cervarix; GlaxoSmithKline, Research Triangle Park, NC) could lead to a robust and sustainable immune system response, says Mahboobeh Safaeian, PhD, an investigator in the NCI's Division of Cancer Epidemiology and Genetics. She states that the Centers for Disease Control and Prevention reports that in 2012, only 53.8% of girls aged 13 to 17 years had initiated HPV vaccination and that only 33.4% of them had received all 3 doses. The findings of the NCI study challenge previous beliefs that protein subunit vaccines require multiple doses to produce a long-lived response, Dr. Safaeian adds.
Their study was based on data from the NCI-funded phase 3 clinical trial testing the efficacy of Cervarix in women from Costa Rica. Although not by plan, 20% of the women in the study received fewer than 3 doses of the vaccine.
Researchers examined the presence of an antibody immune response in blood samples from 78 women, 192 women, and 120 women who received 1, 2, and 3 doses of the vaccine, respectively. They compared the results with data from 113 women who did not receive the vaccine but who had antibodies against the virus in their blood because they previously had been infected with HPV.
Their results demonstrated that 100% of the women in all 3 groups had antibodies against HPV types 16 and 18 for up to 4 years. The levels were comparable for women who received 2 doses of the vaccine 6 months apart and those who had received all 3 doses. Although antibody levels were lower among women who received only 1 dose, the levels appeared stable. In addition, the levels of antibodies in the 1-dose and 2-dose groups were 5 to 24 times higher than those among women who did not receive the vaccine but who had prior HPV infection.
The study indicates that HPV vaccine schedules could potentially be simplified, thereby allowing for less expensive vaccines and easier implementation around the world, particularly in developing countries, in which 85% of cervical cancer cases occur, says Dr. Safaeian. Two HPV doses are currently recommended in some countries; however, more data are needed before a single HPV vaccine could be recommended, she adds. For example, the persistence of an antibody response after a single dose has not been determined for Gardasil (Merck, Whitehouse Station, NJ), the vaccine that is more widely used in the United States and many other countries.