Although human papillomavirus (HPV) vaccines are best known for preventing cervical cancer, a new study from Sweden finds that women and girls who received the immunizations are also less likely to develop precancerous lesions of the vulva and vagina.
The rate of precancerous vulvar or vaginal lesions was 37% lower in women and girls who received at least one dose of HPV vaccine than among study participants who did not, according to a study from Sweden’s Karolinska Institute published yesterday in JAMA Oncology.
People who were vaccinated against HPV before age 17 benefited the most; their rate of vaginal or vulvar precancers was 57% lower than for unvaccinated women.
During follow-up, investigators identified 98 cases of high-grade lesions of the vulva or vagina lesions in vaccinated women, compared with 547 cases in unvaccinated women. That led to an incidence rate ratio (IRR) of high-grade lesions of 0.63, for a vaccine efficacy of 37%. The IRR was 0.43 for women who were vaccinated at age 10 to 16 years.
Vaccines ‘transforming cancer prevention’
“HPV vaccines are transforming cancer prevention,” wrote Yunyang Deng, PhD, first author of the study, and senior author Jiayao Lei, MBBS, PhD, in a joint response to emailed questions from CIDRAP News. “The HPV vaccine is a safe, powerful way to protect our child from cancers.”
The study included 770,000 women born from 1985 to 1998 and living in Sweden from 2006 to 2022. Researchers used Swedish national health registries to follow the participants over time. They considered factors that can affect cancer risk—including age, education, income and maternal medical histories—in their calculations.
What we do see, consistently across several countries, is a sharp drop in HPV infections, precancerous changes, and cancer after vaccination.
Hundreds of millions of doses of HPV vaccines have been administered to girls and boys around the world, and their safety has been monitored carefully, according to the World Health Organization.
“The evidence is very clear,” Deng and Lei said in their email. “Serious side effects are extremely rare, and large studies have found no link to adverse pregnancy outcomes, autoimmune disease, or long-term health problems. What we do see, consistently across several countries, is a sharp drop in HPV infections, precancerous changes, and cancer after vaccination.”
HPV causes at least 6 kinds of cancer
HPV spreads through close skin-to-skin contact. About 80% of women and 90% of men who are sexually active are exposed to the virus. While the immune system takes care of most HPV infections, some infections can become chronic, increasing the risk of cancer.
Jiayao Lei, MBBS, PhD
Jiayao Lei, MBBS, PhD, senior author of the study.
HPV can cause cancers that affect men, as well, including tumors of the penis and anus. HPV is also a major cause of head and neck cancer in both men and women, specifically the oropharynx, the middle part of the throat behind the mouth.
“Studies are consistently showing reductions in precancerous lesions and cancers in these areas following HPV vaccination, indicating the potential of HPV vaccine to save lives and prevent suffering,” said Rebecca Perkins, MD, obstetrician and gynecologist and investigator at the Woman, Mother and Baby Research Institute at Tufts Medical Center who wasn’t involved in the study.
Authors of the new study said they plan to study HPV vaccine effects in other cancers, including in boys. Because oropharyngeal cancers tend to develop later in life, Deng and Lei expect that it will take decades to know if HPV vaccination also prevents cancer of the oropharynx.
Pinpointing whether HPV vaccines prevent oropharyngeal cancer could be difficult, said Mark Einstein, MD, chair of the Department of Obstetrics and Gynecology and Women’s Health at Montefiore Einstein in New York, who was not involved in the new study. HPV causes 90% of cervical cancers but only 70% of oropharyngeal cancers, which also can be fueled by alcohol and tobacco use.
While cervical cancer can be detected early through screening, there are no early detection strategies for oropharyngeal cancer, for which treatment can be very painful.
More than 42 million people in the United States carry at least one strain of HPV that can cause disease, including genital warts or cancer, and 47,000 people a year are diagnosed as having an HPV-linked malignancy.
Some of these cancers are more common than others:
Oral and oropharyngeal cancer: About 59,660 new cases and 12,770 deaths are expected this year, according to the American Cancer Society.
Cervical cancer: About 13,360 new cases are expected be diagnosed by the end of 2025, and 4,320 women will die from the disease.
Anal cancer: About 10,930 new cases are diagnosed each year, along with 2,030 deaths.
Vulvar cancer: About 7,480 cancers of the vulva will be diagnosed and about 1,770 women will die of this cancer, according to the American Cancer Society.
Penile cancer: About 2,190 new cases are projected to be diagnosed, along with 510 deaths.
Vaginal Cancer: About 1,394 cancers were diagnosed in 2022, with 438 deaths in 2023, according to the US Centers for Disease Control and Prevention (CDC).
Finding vulvar and vaginal lesions at the precancerous stage—before they transform into life-threatening cancer—is important, because early detection increases the odds of being cured. Vulvar and vaginal cancers are often treated with laser or excision of affected skin.which can be disfiguring and painful, Perkins said.
“This study shows that HPV vaccination can prevent these lesions in young women, saving them from developing precancers and cancers requiring these difficult treatments,” Perkins said.
Protecting a generation of children
The strongest evidence of the HPV shot’s effectiveness so far is in cervical cancer.
In addition to preventing cervical cancer in vaccinated women and girls, HPV shots also have helped to build herd immunity, which occurs when the levels of virus in a population fall low enough to decrease transmission, said James Campbell, MD, vice chair of the American Academy of Pediatrics (AAP) Committee on Infectious Diseases.
Among women ages 20 to 24—the generation eligible for HPV shots as adolescents—the incidence of cervical precancer fell nearly 80% from 2002 to 2008, according to the CDC. Cervical cancer incidence fell 65% from 2012 to 2019 among women under 25. Death rates from cervical cancer among the same age group fell 62% from 2013-2015 to 2019-2021.
HPV vaccination can prevent these lesions in young women, saving them from developing precancers and cancers requiring these difficult treatments.
Vaccine hesitancy has kept many parents from vaccinating their children. Only 61% of adolescents are up to date on all HPV vaccine doses.
Many other countries have higher rates of HPV vaccination. Scotland has now seen “a generation without cervical cancer due to vaccination,” Perkins said.
Expanding HPV vaccinations to all children
Although the original HPV shots protected girls against four strains of the virus, the vaccines have since been updated to protect against nine strains.
Both the AAP and the American College of Obstetricians and Gynecologists (ACOG) recommend children receive begin the HPV vaccine series between ages of 9 to 12 years, because research shows that’s when kids produce the most antibodies to the virus.
Medical societies recommend two doses for younger teens and three doses for older teens, based on studies of how the immune system reacts to the immunization.
Although research published earlier this month suggests that a single dose of HPV protects children just as well as two, medical societies have not changed their recommendations.