By Megan Brooks
NEW YORK (Reuters Health) Nov 04 - A single dose of human papillomavirus (HPV) vaccine may protect against cervical cancer, according to a randomized trial from Costa Rica.
Women who received one dose of Cervarix - the bivalent HPV vaccine that targets HPV subtypes 16 and 18 responsible for the majority of cervical cancer -- had a strong and durable immune response.
"We found that both HPV 16 and HPV 18 antibody levels in women who received one dose remained stable four years after vaccination," Dr. Mahboobeh Safaeian at the National Cancer Institute (NCI) in Bethesda, Maryland, said in a statement.
"Our findings challenge previous dogma that protein subunit vaccines require multiple doses to generate long-lived responses," she added. They also "suggest promise for simplified vaccine administration schedules that might be cheaper, simpler, and more likely to be implemented around the world," Dr. Safaeian noted.
"This is exciting information, particularly for the third world where there are no Pap smears and cervix cancer is an epidemic," Dr. Robert DeBarnardo, a gynecologic oncologist at the Cleveland Clinic, who wasn't involved in the study, told Reuters Health by phone.
"Cervix cancer is generally one of the leading causes of cancer death in women in the third world. These areas don't have big health care budgets and if we can give one dose of HPV vaccine that can provide a measure of protection, as this study suggests, that's really exciting news," he said.
Dr. Safaeian and colleagues evaluated the magnitude and durability of the immune response to Cervarix by measuring HPV 16/18-specific antibodies in women in the Costa Rica Vaccine Trial (CVT). About 20% of the women in the study did not receive all three doses of the vaccine, not by design.
They focused on 78 women who received one dose, 192 women who received two doses and 120 who got all three doses of the vaccine and compared them to 113 women who did not receive vaccine but had antibodies against the viruses, presumably from natural infection.
According to a report online today in Cancer Prevention Research, all of the women in the three Cervarix groups had antibodies against HPV 16 and 18 for up to four years. Antibody titers were comparable for women receiving two doses six months apart and those receiving the full three doses.
Antibody titers among women who received one dose were lower than among those who received three doses, but the levels appeared stable, suggesting that these are lasting responses, the researchers say.
They also note that antibody levels in women from the one- and two-dose groups were five to 24 times higher than those in women who didn't receive vaccination, but had prior HPV infection.
"It's interesting that we are seeing immunity with only one or even two doses of the vaccine because typically we've relied on three doses to boost the immune system enough to see a response," Dr. DeBarnardo told Reuters Health.
Dr. Safaeian said it's important to note that "persistence of antibody responses after a single dose has not been evaluated for Gardasil, the quadrivalent HPV vaccine that is more widely used in the United States and many other countries."
For Gardasil, three doses vaccine are currently recommended, "but it's very difficult to get children in to have these three vaccines; many don't complete the series," Dr. DeBarnardo said. "It would be very interesting to go back and look at titers now or five or 10 years from now and see what the rate of cervical dysplasia is in this population."
He wonders, "If we are providing only partial immunity and at the same time pulling back on Pap smear screening, what is that going to mean 20 years from now with the rates of cervix cancer in this country?"
The study was sponsored by the NCI with support from the National Institutes of Health Office of Research on Women's Health and the Ministry of Health of Costa Rica. The HPV vaccine was provided by GlaxoSmithKline Biologicals. Dr. Safaeian declared she has no conflicts of interest. She was traveling and unreachable before press time.
Cancer Prev Res 2013.
Reuters Health Information © 2013