According to the Centers for Disease Control (CDC), about 43 million human papillomavirus (HPV) infections were reported in 2018.
In nearly all (nine out of 10) cases, HPV infection resolves on its own within two years without posing any health problems.
In rare cases, however, HPV infection causes cells to undergo modifications that can result in cervical cancer, a major public health concern.
Cervical cancer typically occurs in people over the age of 30 and often affects women during their reproductive years.
The World Health Organization estimates that a large majority of cervical cancer (more than 95%) is due to HPV infection and as many as 93% of cervical cancers could be prevented by HPV vaccination and screening.
However, only 15% of the eligible global population of women have been vaccinated.
One key barrier to vaccine uptake is the challenge of scheduling and delivering multiple doses of the vaccine. HPV vaccines are typically given as a series, starting at age 11 or 12 with the doses scheduled six months apart.
Recent evidence indicates that a single dose of the vaccine might be effective in protecting against HPV. Could a one-dose regimen make uptake easier and reduce the rates of cervical cancer?
That was the question that Ruanne Barnabas, MD, chief of the Division of Infectious Diseases in the Department of Medicine at Massachusetts General Hospital and professor of Medicine at Harvard Medical School, and her team investigated in a recent study of young women in Kenya.
The team found that after three years, a single dose of the HPV vaccine was both effective and efficacious in preventing HPV infection.
The findings, which were published in Nature Medicine, provide further scientific evidence that one-dose of the vaccine is sufficient, which could help in changing vaccine distribution programs and increasing uptake in the areas that need it most.
Barriers to HPV Vaccination: Accessibility and Frequency
For years, Barnabas has focused her research on identifying barriers to accessing health interventions and simplifying health care delivery in order to reduce global rates of infectious diseases.
By conducting mathematical computer modeling, she and her research team realized they could effectively eliminate cervical cancer by increasing HPV vaccine rates worldwide.
With this in mind, they sought to answer the question: Can we improve vaccination rates by simplifying the vaccine delivery process?
“We were inspired by the data and findings from a vaccine trial in Costa Rica, which showed that individuals who received a single dose of the [HPV] vaccine had about the same effectiveness as people who received two or three doses,” she explains.
“Since that study used observational data, we knew we had to do a randomized controlled trial (RCT) to robustly estimate effectiveness of single-dose HPV vaccination.”
A Trial to Study Effectiveness of HPV Vaccination
Barnabas and her team traveled to Kenya.
When they visited the wards where patients with cervical cancer were receiving treatment—many of them women with families—they knew that their trial should be conducted in a setting where it could make a real impact.
Cervical cancer is common in Kenya, Barnabas explains. “When you're in any room and you ask someone, ‘Who knows someone who has had cervical cancer or who has died from cervical cancer?’ Hands always go up."
The team worked with statisticians to estimate the number of participants they would need to enroll, and collaborated with health officials in Kenya who would be willing to change the HPV vaccination schedule to a one-dose regimen, but would need data first.
The team enrolled 2,275 participants between the ages of 15-20 and randomly assigned them to receive one dose of one of two types of HPV vaccine. A nonavalent vaccine, which protects against nine HPV types including seven types that cause 90% of cervical cancers, and a bivalent vaccine, which protects against two HPV types that cause 70% of cancer cases.
Clinicians collected cervical swabs from participants every six months, which were tested for HPV DNA. Participants were followed for 36 months (about three years) to analyze vaccine efficacy.
The Clinical Implications of the Findings
After three years, the results showed that the single dose of both the bivalent and nonavalent HPV vaccines were highly efficacious, with a vaccine efficacy of 98%.
Additionally, the nonavalent vaccine had a vaccine efficacy of 96% for the seven high-risk types of HPV it targets.
To make a true public health impact, vaccines must be both efficacious – shown to work in a controlled setting such as a research study – and effective – which means they work in a real-world setting where other facts come into play.
After reviewing the evidence, including the pivotal findings from this trial, the World Health Organization is now recommending single-dose HPV vaccination for girls and boys aged 9 to 20 years. To-date, thirty-two countries have adopted this single-dose HPV vaccination policy.
While the results are a step along the right path, Barnabas says more work is needed to improve equitable access to vaccines and other healthcare services.
"As providers, we really need to think about whether we’re delivering services in a way that are easy for people to access,” she explains. “Can people get the vaccines in a convenient location, at a convenient time? Do they have appointments? Do they have transportation?"
“It's also on us as providers to offer the services in a way that they are accessible and meet the needs of the people who are receiving those services”
About the Mass General Research Institute
Research at Massachusetts General Hospital is interwoven through more than 30 different departments, centers and institutes. Our research includes fundamental, lab-based science; clinical trials to test new drugs, devices and diagnostic tools; and community and population-based research to improve health outcomes across populations and eliminate disparities in care.
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