Single dose of HPV vaccine may be enough
Just one dose of the HPV vaccine Cervarix appears to provide enough of an immune response to protect women from two strains of human papillomavirus (HPV) and ultimately cervical cancer, according to a new study published Monday.
HPV is the most common sexually transmitted infection (STI), according to the U.S. Centers for Disease Control and Prevention (CDC). The infection, transmitted through genital contact, is the primary cause of cervical cancer, which affects about 10,300 women in the United States each year. It causes about 275,000 deaths annually worldwide and is a leading cause of cancer deaths among women in low-income countries, according to the World Health Organization.
“Cervical cancer is a major cause of public health concern, especially in less developed countries where about 85% of cervical cancer occurs,” says study author Mahboobeh Safaeian. “The reason for that is mainly because of lack of screening infrastructure offered.”
Safaeian and her team followed a group of women in Costa Rica who were participating in the National Cancer Institute-funded phase III clinical trial testing the efficacy of Cervarix. About 20% of these women did not complete the three-dose vaccine regimen. Safaeian compared the groups of women who had received one, two and three doses of the vaccine, as well as women who had antibodies from having been naturally infected.
The researchers found that women vaccinated with a single dose of Cervarix, as opposed to the current CDC recommendation of three, had antibodies against HPV that remained stable in their blood after four years. The findings suggest that the common recommendation for three doses may not be necessary to ensure long-lasting antibodies that prevent HPV. Safaeian, a researcher for the National Cancer Institute’s Division of Cancer Epidemiology & Genetics, Infections and Immunoepidemiology, says this could have significant implications for women across the world by simplifying the logistics and costs of vaccinations.
“This vaccine is about $130 a dose … It’s just not feasible in a lot of undeveloped countries,” Safaeian explains.
Even in the United States, where vaccinations are easily accessible and covered under health insurance and federal programs for children, many women are not getting all three doses. In 2012, only about half of girls between ages 13 and 17 started the HPV vaccination regimen and only about a third had received all three doses, according to the CDC.
Dr. Kevin Ault, a physician and professor at the Emory University Department of Gynecology and Obstetrics, emphasizes that it is always easier to get people into the office for a one-time vaccination. In countries outside the United States, one stop may be the only option.
“Certainly if you’re in South Asia or Africa, where you have a high burden of cancer and screening is expensive, a single dose vaccine would really be a game changer,” says Ault, who worked on the clinical trials that led to the approval of the first HPV vaccine Gardasil, which protects against four strains of HPV.
However, while this new study reveals promising results for one and two doses of Cervarix, Ault does not see this changing the standards in the United States anytime soon. He said he believes further research will be conducted in the following years, for Cervarix and also for Gardasil, the more common of the two HPV vaccines in America. Gardasil has not yet been tested for the efficacy of less than three doses. Until then, Ault plans to stick to the CDC recommendation of the three-dose vaccine for his patients.
Safaeian also stresses that this research is still at the beginning stages. She notes that long-term protection is one of the outstanding questions.
“The data we have thus far only goes up to four years,” Safaeian emphasized. “Ideally, you would want protection to last 10 to 15 years. So, we still are not there yet – the studies have not gone that far.”
Some countries, such as Chile, have already implemented a two-dose vaccination plan, but Safaeian said that it’s still too early to tell whether it is sufficient for long-term protection.
Safaeian continues to move forward with her research, following the same participants to see whether the antibody stability extends beyond the four years. She said that while it’s not over yet, her team has “provided some intriguing research that could help discussions of what should be the next step for evaluating number of doses.”
The new study was published Monday in Cancer Prevention Research, a journal of the American Association for Cancer Research.