Over the years, NPR (and our blog) have reported on the global effort to eliminate cervical cancer with the HPV vaccine introduced in 2007.
Human papillomavirus, or HPV, is a group of over 200 viruses that are common in humans. Most types don’t cause any problems, but some can develop into diseases such as genital warts or cancer, and 99% of the world’s 660,000 annual cases of cervical cancers are caused by two strains, which can be sexually transmitted.
Women ages 35 to 44 are most frequently diagnosed with cervical cancer; administering the vaccine to teen and preteen girls can confer protection before exposure to HPV.
The annual death toll of the world’s fourth most common cancer is 350,000. And more than 90% of these deaths occur in low- to middle-income countries.
The vaccine stimulates the body to produce antibodies that, in future encounters with the HPV virus, bind to the virus and prevent it from infecting cells. Initially, two or three doses of the vaccine were called for — problematic in countries where access to health care may be limited. In 2022, the World Health Organization recommended a single dose as sufficient to afford protection.
This year, in March, the Global Cervical Cancer Elimination Forum convened in Cartagena, Colombia, to urge all interested parties to amp up their efforts, with a group of organizationscollectively allocating $600 million in additional funding, including the World Bank, UNICEF and the Bill & Melinda Gates Foundation (which is a funder of this blog and NPR.) If the goals are fully realized, according to WHO, “the world could [potentially] eliminate a cancer for the first time.”
As of 2022, only about a fifth of girls ages 9 to 14 had received a dose, falling well short of WHO’s goal of reaching 90% of 15-year-old girls by 2030.
Here’s what’s been happening since WHO’s single-dose recommendation.
Since the World Health Organization issued its guidance to drop the number of HPV vaccine doses for girls ages 9 to 14 from three to just one, close to 60 countries, including many low- and middle-income countries, have created one-dose HPV immunization programs.
“One dose is a game changer, says Cathy Ndiaye, technical adviser for HPV vaccination programs in Africa and Asia at the global health nonprofit PATH.
“We have big, big countries that aren’t known for their amazing health care systems, but are prioritizing this, says Greg Widmyer, senior adviser in the Global Development Division of the Bill & Melinda Gates Foundation, which funded some of the clinical trials. “India, the Democratic Republic of Congo [and] Pakistan are all in the planning phases to introduce [the lowered dose regimen] over the next 12 to 18 months.
The March meeting also highlighted the need for cervical cancer screening. That’s because early diagnosis is critical. If the cancer is diagnosed after it has spread to other organs the five-year survival rate is only 19%, according to the American Cancer Society.
Hopes are high for the single-dose programs. “The optimization of the [newly revised] HPV schedule is expected to improve access to the vaccine,” WHO said in a release when it announced the new recommendation. “offering countries the opportunity to expand the number of girls who can be vaccinated and alleviating the burden of the often complicated and costly follow-up required to complete the vaccination series.”
Currently, of the 73 low- and middle-income countries that get vaccine funding assistance from Gavi, the Vaccine Alliance, only 44% have included the HPV vaccine in their immunization schedules. Reasons for that include cost, supply constraints and a lack of infrastructure for vaccinating preteen and teenage girls, says a spokesperson for Gavi, a nonprofit group that helps fund the cost of vaccines in poorer countries.
But progress is slowly inching up. The latest UNICEF data on the HPV vaccine, released this summer, is that vaccination among girls 9 to14 has marginally increased by 1% in 2022 to 2% in 2023. The slight increase, according to UNICEF, is largely due to the introduction of a one-dose HPV vaccination program in Bangladesh in 2023.
The single dose saga
The idea that a single dose could be protective against cancers caused by HPV came from a 2004 clinical trial in Costa Rica. The trial looked at outcomes from three shots, the initial dosing schedule for the vaccine.
The Costa Rica trial was funded by the U.S. National Institutes of Health. About 20% of women received fewer than three vaccine doses, typically because they didn’t return for the subsequent doses, says Ruanne Barnabas, now chief of the division of infectious diseases at Massachusetts General Hospital, who led a confirmatory one-dose trial in Kenya beginning in 2018.
The researchers continued to collect cervical and blood samples from participants seven, nine and 11 years after vaccination. They found that regardless of the number of doses, women who got the HPV vaccine had very few infections of the strains that can cause cervical cancer.
Results of the first randomized controlled trial of single-dose HPV vaccine were published in the New England Journal of Medicine Evidence in April 2022 with the final results published in Nature Medicine in December 2023. The two studies showed greater than 97% efficacy against the HPV16 and HPV 18 strains at 36 months from a one dose vaccination among women in Kenya
An additional trial in Tanzania confirmed the effectiveness of the one-dose vaccine.
Why does the HPV virus respond to a smaller number of vaccine doses? Says Barnabas: “HPV has a hard time establishing an infection compared to other pathogens, and even a small concentration of antibodies stimulated from a single dose of the vaccine can prevent cervical cancer from developing.”
Advocacy efforts have focused both on transitioning to a one-dose regimen as well as introducing the vaccine to new countries.
The United States has not issued a one-dose HPV vaccine recommendation; the CDC convened a working group in June to consider the issue. According to a CDC report last month, 61% percent of 13-to-17-year-olds in the U.S. have received the two doses.
Challenges include convincing parents
Because the vaccine isn’t well known and targets a sexually transmitted disease, PATH’s Cathy Ndiaye says a great deal of planning is necessary to fully implement it even after a country has signed on. That includes training health workers to administer and explain the vaccine; engaging with girls, parents, community leaders and often religious leaders to explain that the vaccine is not a contraceptive but instead helps to protect against a sexually transmitted disease that could affect them later in life.
Ndiaye says PATH has found that girls in the target age range are often still in primary school, which makes school-based clinics a strong choice for vaccine administration. “Many girls drop out of secondary school, so vaccinating before they leave school can help protect so many girls,” she says.
Ndiaye says getting parents to allow their daughters to be vaccinated can be difficult, which is why PATH and other advocacy groups have created planning programs when a country approves the vaccine. “It’s important to address the rumors and negative perceptions about the vaccine,” she says. “Some caregivers worry about fertility and reproductive health implications.”
Women’s health advocates are also playing a role. In Nigeria, where the vaccine was first rolled out last year, Juliet Iwelunmor, a professor of medicine at the Washington University School of Medicine in St. Louis, is piloting a program to encourage conversations between mothers and daughters about the importance of vaccination and screening. Iwelunmor is dedicating the program to the memory of her sister-in-law, whom she calls “the heart of the family,” who died two years ago of cervical cancer in Lagos. The pilot includes about 300 mother-daughter pairs who receive information about the vaccine and screening with facilitators helping with the discussion.
After the pilot ends, Iwelunmor plans a clinical trial to evaluate the impact of these conversations on screening and vaccination rates. She’s proud that her sister-in-law’s daughter, now 14, received her HPV vaccine when the shot was first available in Nigeria. “Now we know she won’t have to go through what her mother did,” Iwelunmor says.
Fran Kritz is a health policy reporter based in Washington, D.C., and a regular contributor to NPR. She also reports for the Washington Post and Verywell Health. Find her on X: @fkritz
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