WASHINGTON — One HPV vaccination appears to be as effective as two doses at preventing the viral infection that causes cervical cancer, researchers reported Wednesday.
HPV, or human papillomavirus, is very common and is transmitted through sexual contact. Most HPV infections go away on their own, but some persist, causing cancers that appear years later, including cervical cancer in women and rarer cancers in both women and men.
HPV vaccination has been recommended for girls in the United States since 2006, and the country is already count fewer cases of precancerous cervical lesions among women in their 20s, the first age group to receive the vaccine when they were teenagers or teenagers.
But cervical cancer kills about 340,000 women worldwide each year, and new findings from a major study in Costa Rica could help spur global efforts to protect more girls and young women in hard-to-reach low-income countries.
The study, conducted by the US National Cancer Institute, involved more than 20,000 girls aged 12 to 16 years. The researchers tested two different HPV vaccines used around the world, resulting in half of the girls receiving one shot and the rest receiving the other. Then, six months later, half of the girls received a second dose of their assigned vaccine, and the rest received an unrelated childhood vaccine instead.
They were followed for five years, undergoing regular cervical tests for the most cancer-prone strains of HPV. Infection rates were compared to a separate unvaccinated group.
One HPV vaccine provides about 97% protection, similar to two doses, researchers from the NCI and Costa Rica's Biomedical Research Agency concluded. The results were published in the New England Journal of Medicine.
Previous studies have shown that a single dose may work, but the new findings support strong protection for at least five years, Dr. Ruann Barnabas, an infectious disease specialist at Massachusetts General Hospital, wrote in an accompanying editorial.
“We have the evidence and tools to eliminate cervical cancer. All that remains is the collective will to implement them fairly, effectively and now,” wrote Barnabas, who was not involved in the Costa Rica study.
In the United States, most girls and boys are recommended to get two HPV vaccinations starting at age 11 or 12, because the virus can also cause head and neck and other cancers. Catch-up vaccinations are recommended for all individuals under 26 years of age who have not been vaccinated. The Centers for Disease Control and Prevention reported that about 78% of children ages 13 to 17 have received at least one dose.
But globally, the World Health Organization estimates that fewer than a third of teenage girls have been vaccinated, and the agency has already begun recommending one or two doses to extend protection.
The new study did not provide any information about HPV-related cancers outside the cervix, and the researchers warned that longer-term monitoring is needed.
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