Researchers say that a single dose of the HPV vaccine may be good enough for protection from the sexually transmitted infection. Photo by marcolohpsoares
Women getting vaccinated against the cancer-causing human papillomavirus -- HPV -- now need two or three shots, but an African clinical trial suggests a single dose is just as effective.
The finding could speed up the immunization process in developing countries with high levels of HPV-related cancers and protect many more women more quickly.
"These findings are a gamechanger that may substantially reduce the incidence of HPV-attributable cervical cancer and positions single-dose HPV vaccination as a high value and high impact public health intervention that is within reach for us," said Sam Kariuki, acting director general of the Kenya Medical Research Institute, in Nairobi.
The trial included 2,275 sexually active women in Kenya between 15 and 20 years of age. The women were randomly assigned a vaccine therapy and were followed from December 2018 to June 2021.
To participate, they needed to have had no more than five lifetime sexual partners, be unvaccinated for HPV, and HIV-negative.
In all, 760 participants received a so-called bivalent vaccine that covered two strains of HPV, 16 and 18.
A similar number received a nonavalent vaccine that covered seven HPV strains: 16, 18, 31, 33, 45, 52 and 58.
The rest received a vaccine that protects against meningococcal meningitis.
After 18 months, both HPV vaccines were 97.5% effective against HPV 16 and 18. Seven in 10 HPV cases involve these two strains.
The nonavalent vaccine was 89% effective against five other strains, as well. Even if women tested positive for one strain of HPV, the vaccine protected them from other strains of the virus.
"The single-dose vaccine was highly effective at 18 months for HPV vaccination," said study co-leader Ruanne Barnabas, a professor of global health at the University of Washington School of Medicine, in Seattle. "The single-dose efficacy was the same as multiple doses."
Her team said more studies need to be done to find out how long the protection lasts.
According to study co-leader Dr. Nelly Mugo, "This trial brings new energy to the elimination of cervical cancer. It brings great hope to the women living in countries like Kenya, who have a high burden of the disease."
Mugo is an associate research professor at the University of Washington and a senior scientist at the Kenya Medical Research Institute.
Worldwide, cervical cancer kills a woman every two minutes, and Africa bears 80% of the burden.
Barnabas said the trial could help the World Health Organization reach its goal to have 90% of 15-year-old girls vaccinated against HPV by 2030.
A single-dose vaccine would simplify logistics and lower costs, she noted, adding that women have been given multiple doses of the vaccine because of gaps in evidence for the effectiveness of a single-dose vaccine.
HPV is a common virus spread by intimate contact. Most sexually active men and women will be infected with HPV during their lives. For most, the infection clears on its own. But for others, the virus can lead to reproductive cancers, most commonly cervical cancer.
The U.S. Food and Drug Administration approved the first HPV vaccine 15 years ago and two others have since been introduced.
The Gardasil-9 vaccine is recommended for boys and girls at 11 and 12 years of age, though it can be given through age 45.
But use has been low in areas like Kenya with high rates of cervical cancer.
The findings were presented recently at the International Papillomavirus Conference in Toronto. Research presented at meetings should be considered preliminary until published in a peer-reviewed journal.
The U.S. Centers for Disease Control and Prevention has more on human papillomavirus.
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