Results from the Costa Rica HPV 16/18 Vaccine Trial indicate that 4-year efficacy against 12-month HPV 16/18 persistent infection was similarly high among women who received one, two, or the recommended three doses of the bivalent HPV16/18 L1 virus-like particle vaccine (Cervarix). The findings suggest that vaccination schedules of two or even one HPV vaccine dose could simplify the logistics and reduce the cost of vaccination in the developing world, where more than 85% of cervical cancers occur. The study results were published in Cancer Prevention Research.1
Mahboobeh Safaeian, PhD, an Investigator in the Division of Cancer Epidemiology and Genetics at the National Cancer Institute, and colleagues analyzed data from the National Cancer Institute–funded phase III Costa Rica HPV 16/18 Vaccine Trial trial to look for the presence of an immune response to the HPV 16/18 vaccine, which was measured by antibody levels. About 20% of the women in the study received fewer than three doses of the vaccine, not by design. Blood samples were drawn from 78, 192, and 120 women who received one, two, and three doses of the vaccine, respectively. The researchers then compared the results with data from 113 women who did not receive the vaccine, but had antibodies against the viruses in their blood because they were infected with HPV in the past.
The researchers found that 100% of the women in all three groups had antibodies against HPV 16 and 18 in their blood for up to 4 years. In addition, antibody levels were comparable for women receiving two doses 6 months apart and those receiving the full three-dose regimen. Although antibody levels among women who had received one dose of the vaccine were lower than among those women who had received three doses, the levels appeared stable, suggesting that these are lasting responses.
“The findings suggest that antibody titers induced by two or three vaccine doses may be substantially higher than needed for long-term protection,” wrote the researchers. The study also found that the levels of antibodies in women from the one- and two-dose groups were 24 times higher than the levels of antibodies in women who did not receive the vaccine, but had prior HPV infection.
“We hope to expand our study to include a longer follow-up because with this vaccine, and probably any other vaccine, you want the protection to last long-term, and we are definitely interested in showing what happens over the next 4 years and even 10 years,” said Dr. Safaeian. ■
Disclosure: Dr. Safaeian reported no potential conflicts of interest. The trial was sponsored by the NCI with funding support from the National Institutes of Health Office of Research on Women’s Health, and the Ministry of Health of Costa Rica. GlaxoSmithKline provided the vaccine for the study.
1. 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 6:1242-1250, 2013.