Vaccine for HPV, the nation’s most common sexually transmitted infection, proves effective

The nation’s most common sexually transmitted infection appears to have an effective, long-term vaccine that continues to reduce cancer risk, a new study found.

New research published this week in the journal Pediatrics builds on growing evidence about the efficacy of vaccination against HPV, which is most often spread through vaginal, anal or oral sex and can result in genital warts. For most people who get HPV, the virus goes away on its own without any effect, but for others, it can lead to certain cancers. 

Researchers affiliated with the pharmaceutical company Merck spent 10 years following nearly 1,300 people vaccinated between age 9 and 15 with Merck’s Gardasil 9, which protects against nine strains of HPV. About 970 girls and 300 boys from 13 countries, spread across five continents, received the vaccine’s approved three-dose regimen, which typically starts in adolescence.

“This should be enormously reassuring to parents: Yet another study showing that this vaccine is safe and it’s effective,” said Dr. Paul Offit, the director of the vaccine education center at the Children’s Hospital of Philadelphia and a professor of pediatrics at the University of Pennsylvania School of Medicine, who was not affiliated with the study. “And that effectiveness lasts at least 10 years, which is exactly what you would have expected given that the problems you’re worried about, whether it’s cancer or genital warts, take a fairly long time to evolve.”

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HPV vaccines have been administered in the U.S. since 2006, according to the Kaiser Family Foundation, a nonpartisan health policy research group. Gardasil 9 was approved in 2014. Hawaii, Rhode Island, Virginia and the District of Columbia have varying laws requiring HPV vaccines for school entry, generally for middle schoolers.

HPV causes about 80% of cervical cancers, which lead to about 12,000 women dying each year, the Centers for Disease Control and Prevention estimates. Since HPV vaccines began being used in the U.S., HPV infections from the strains that cause most cancers and genital warts have dropped 88% among teen girls and 81% among young adult women. Among vaccinated women, there’s been a 40% drop in cervical cancers caused by HPV strains associated with the illness. The decline in infections is attributed to more widespread use of the vaccine.

Head and neck cancers derived from HPV, however, have steadily risen, particularly among men, prompting concern among health professionals to inoculate more boys.

In the Pediatrics study, conducted from August 2009 to April 2021, testing found the majority of participants still had HPV antibodies in their system a decade after being vaccinated, suggesting long-term protection against the nine virus types it’s designed to combat.

A decade after the third dose, neither boys nor girls showed cancer-causing cells derived from strains of HPV, nor did they have genital warts derived from the types of HPV they were vaccinated against.

Growing body of research shows effectiveness of HPV vaccines

The study published this week adds to ongoing research around HPV vaccines, including a prior eight-year interim study.

The findings indicate the vaccine protected more than 90% of recipients for a full decade, suggesting booster shots are not yet needed, said Dr. Alain Luxembourg, the executive director of clinical research at Merck and a study author.

“It’s really an ideal situation for vaccines,” said Luxembourg, who helped develop the nine-valent Gardasil vaccine.

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The study didn’t use a control group, or people who didn’t receive treatment for HPV. Instead, it relied on comparing prior vaccine trials, researchers added.

The low incidence of infection and disease related to the HPV vaccine isn’t likely tied to participants being sexually inactive, researchers said. Participants contracted other STIs, including HPV types not covered by the vaccine, during the study.

Close to a third of the original participants in the study dropped out over time, something researchers expected as their young subjects navigated school, jobs or family issues. That left about 920 people who were tracked for the entire length of the study.

Researchers studied only the three-dose regimen of Gardasil 9, though they acknowledged that two-dose regimens may be easier to implement globally and already are licensed and recommended for children ages 9 to 15. Prior research on two-dose HPV vaccine regimens shows they also provide long-term protection.

Merck has distributed over 444 million doses of Gardasil, which protects against four types of HPV, and over 203 million doses of Gardasil 9, the company said.

Eduardo Cuevas covers health and breaking news for USA TODAY. He can be reached at [email protected].