New research shows that one HPV vaccine shot may be effective for up to four years, but not all women have equal access to these life-saving medications.

A single dose of the human papillomavirus (HPV) vaccine can spur the creation of antibodies that fight the virus for up to four years, according to a new study published in Cancer Prevention Research.

The new findings suggest that a single dose of the vaccine may be enough to protect women against the virus that causes 70 percent of all cases of cervical cancer.

HPV vaccines, sold under the brand names Cervarix and Gardasil, are typically delivered in three doses. The U.S. Centers for Disease Control (CDC) estimates that only 53.8 percent of girls ages 13 to 17 began HPV vaccinations by 2012, and only one third of them received all three doses. HPV is the most common sexually transmitted infection, according to the CDC.

Myth Busted: Still No Evidence to Support Vaccine-Autism Link »

Researchers had been conducting a phase III clinical trial in Costa Rica funded by the National Cancer Institute (NCI) to test the effectiveness of Cervarix. About 20 percent of the women in the study didn’t receive all three doses.

Despite this, researchers found that all women who received at least one dose of the vaccine had stable levels of antibodies to fight HPV 16 and 18 strains in their blood for up to four years after their first treatment.

“Our findings suggest promise for simplified vaccine administration schedules that might be cheaper, simpler, and more likely to be implemented around the world,” Mahboobeh Safaeian, an investigator in the Division of Cancer Epidemiology and Genetics with the NCI, said in a press release.

“Vaccination with two doses, or even one dose, could simplify the logistics and reduce the cost of vaccination, which could be especially important in the developing world, where more than 85 percent of cervical cancers occur and where cervical cancer is one of the most common causes of cancer-related deaths,” Safaeian added.

Safaeian said that while the team’s findings are “quite intriguing and show promise,” more data needs to be collected and examined before the official vaccination schedule can be changed. This includes evaluating the effectiveness of Gardasil, the most widely used HPV vaccine in the U.S.

Learn Why the CDC Says Young Gay Men Need the HPV Shot, Too »

Women who receive HPV or any other kind of vaccination are strongly urged to complete their full vaccination course as directed by their doctors.

Beth Meyerson, a health policy expert at the Indiana University School of Public Health in Bloomington, and colleagues interviewed 15 professionals working in various public and private cancer centers. They found holes in the system that prevent the disadvantaged and minority patients from getting the care they need.

“We focus on cervical cancer because it is likely the ‘low-hanging fruit’ opportunity to beat a cancer in this generation,” Meyerson said in a statement. “We have the tools of HPV vaccination, screening, and treatment, but uninsured women and women of color experience huge health disparities. This is the signal that we have a health system problem.”

Meyerson said coordinated efforts between state departments of health and the federal Medicaid program—like initiatives in place in Kentucky to expand Medicaid to low-income adults—are one possible solution to increase coverage and keep costs low.

“The challenge is to help separately funded programs work together—a very tall charge and one that public health administration grapples with perennially,” she said.