A new study has found that just one dose of the HPV vaccine may work as well as two doses to protect against the virus that causes cervical cancer.
This discovery could help protect more girls and young women around the world, especially in countries where getting two shots is harder.
HPV, or human papillomavirus, is a common virus that spreads through sexual contact. In many cases, the virus goes away on its own. But sometimes it stays in the body and causes cancer years later. The most well-known type of cancer linked to HPV is cervical cancer in women. However, HPV can also cause less common cancers in both men and women.
In the U.S., the HPV vaccine has been recommended for girls since 2006. Since then, the number of young women with early signs of cervical cancer has dropped. This shows that the vaccine works.
But cervical cancer still kills about 340,000 women around the world each year. Many of these women live in low-income countries where it’s difficult to give multiple vaccine doses.
The new study, led by the U.S. National Cancer Institute, included over 20,000 girls in Costa Rica between the ages of 12 and 16. Researchers tested two kinds of HPV vaccines that are used in different parts of the world.
Some girls got one type of vaccine, while others got the second type. Six months later, half of the girls received a second dose of their assigned HPV vaccine. The other half received a different vaccine that wasn’t related to HPV, as a control.
The girls were then tracked for five years. During that time, they received regular cervical tests to check for HPV infections that are known to lead to cancer. Researchers compared the infection rates to a separate group of girls who had not been vaccinated at all.
The results were surprising. A single HPV shot gave about 97% protection—almost the same as two shots. These results were published in the New England Journal of Medicine. The findings give strong evidence that one shot can provide long-lasting protection, at least for five years.
Dr. Ruanne Barnabas, an infectious disease expert at Massachusetts General Hospital, praised the study in an editorial. She was not part of the research but said the results show we now have the tools to eliminate cervical cancer. The challenge is to use these tools in a fair and effective way around the world.
In the U.S., two doses of the HPV vaccine are recommended starting at age 11 or 12 for both girls and boys. This is because HPV can also cause cancers of the head, neck, and other parts of the body. People who didn’t get the vaccine earlier can still get it up to age 26. According to the CDC, about 78% of U.S. teens aged 13 to 17 have received at least one dose.
Worldwide, however, fewer than one-third of teenage girls have been vaccinated. To make the vaccine more accessible, the World Health Organization already supports either one or two doses.
The study did not look at cancers other than cervical cancer, and researchers say more time is needed to see how long the protection lasts. Still, the results are encouraging. A one-shot vaccine could make it much easier to protect girls everywhere and save lives.
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The study is published in New England Journal of Medicine.
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