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A single dose — rather than the recommended three — of a vaccine against the sexually transmitted human papillomavirus (HPV) may be enough to ward off cervical cancer, researchers said Monday. The findings could lead to simpler delivery and lower costs, possibly increasing the number of young people who get vaccinated, said their report in the journal Cancer Prevention Research.
The HPV vaccine is recommended for girls and boys before they become sexually active, but U.S. research from 2012 showed that only 33 percent of U.S. female teens and fewer than 7 percent of U.S. male teens got the recommended three doses.
"Our findings suggest promise for simplified vaccine administration schedules that might be cheaper, simpler and more likely to be implemented around the world," said Mahboobeh Safaeian, an investigator in the Division of Cancer Epidemiology and Genetics at the National Cancer Institute in Maryland.
But there are still impediments to widespread use of the vaccine, including the stigma surrounding vaccinating children against sexually transmitted infections and language barriers that prevent many from going to a doctor.
The study focused on a population of nearly 7,500 women ages 18 to 25 in Costa Rica. Although all were supposed to receive the recommended three doses of the HPV vaccine at different times, about 20 percent of participants did not.
So researchers analyzed blood samples from a group of 78 who got one dose, compared with groups of 120 to 192 that received two or three doses as planned. They found that all the women in all three groups had antibodies against virulent strains of HPV, known as 16 and 18. The antibodies persisted in their blood for up to four years, which is about as long as researchers have expected the vaccine to be effective.
The levels of antibodies also appeared stable over time, even though they were slightly lower in the single-dose group, suggesting "these are lasting responses," said the study. The vaccine used in the study was Cervarix, made by the British pharmaceutical giant GlaxoSmithKline.
"GSK is continuing to review findings from this trial and is committed to ensuring regulatory authorities and public-health officials have access to this information," a company spokesman told Agence France-Presse.
Study authors said antibody responses after a single dose have not been evaluated for Gardasil, the HPV vaccine made by Merck that is more widely used in the United States and many other countries. More research is needed before any formal changes can be decided, but Safaeian said the findings could have far-reaching impact across the globe.
"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," said Safaeian.
Cervical cancer is the second most common cancer in women worldwide and causes 500,000 new cases and 250,000 deaths each year, according to the World Health Organization. In the U.S., about 79 million people are infected with the virus, and the Centers for Disease Control and Prevention says that at current rates, 14 million people will become infected each year. Of those new infections, about 26,000 new cancers occur each year.
It remains to be seen how lowering the dosage requirements would affect the universal implementation of the vaccine.
Al Jazeera and AFP
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