‘Reassuring’: Single dose of 9-valent HPV vaccine effective
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Key takeaways:
- A single-dose HPV vaccine schedule could improve coverage where resources are limited.
- New study results suggest one dose provides persistent and stable antibody responses for up to 2 years.
One dose of the 9-valent HPV vaccine generated a sustained immune response against two prominent cancer-causing types of the virus for up to 2 years, according study findings published in Pediatrics.
The results “[add] to ongoing evidence being reviewed by national and international guideline bodies that are considering one-dose HPV vaccine schedules” for areas with limited resources where two- to three-dose HPV vaccine schedules pose logistical challenges.
“Fortunately, due to advances in science and medicine over the past several decades, multiple approaches now exist to prevent HPV-related cancers,” Vikrant Sahasrabuddhe, MBBS, MPH, DrPH, program director in the Division of Cancer Prevention at the NIH’s National Cancer Institute, told Healio.
“HPV vaccination is a highly effective approach and is currently strongly recommended for ages 9 through 26 (years) as a way to prevent the development of HPV-related cancers before they develop,” Sahasrabuddhe said. “Yet, uptake rates of the full two- or three-shot series of the HPV vaccine have been below our expectations, and researchers are exploring the utility of expanding coverage to every eligible individual with at least one dose of the HPV vaccine.”
Sahasrabuddhe said several previous studies have suggested that a single dose of HPV vaccine may be effective, especially against the high-risk HPV16 and HPV18 types.
“We wanted to contribute evidence from the United States to the expanding set of studies globally on the use of single-dose schedules to expand the reach of HPV vaccination uptake to as many individuals as we can,” Sahasrabuddhe said.
Past studies conducted in the United States have found that although the rate of teenagers vaccinated against HPV is improving, a significant number of parents remain hesitant about their children receiving the vaccine.
Research has also found that Americans’ awareness that HPV causes cancer has declined, and that reframing vaccine discussions to focus on the vaccine’s ability to reduce the risk for cancer may improve uptake.
For their study, Sahasrabuddhe and colleagues enrolled 201 healthy 9- to 11-year-old girls and boys in the Tucson, Arizona, and Los Angeles areas, who received an initial single dose of the 9-valent vaccine before receiving a booster dose 2 years later and an optional third dose 6 months following the booster. They also collected blood samples at baseline and then every 6 months to measure antibodies.
“The results were not surprising but were reassuring,” Sahasrabuddhe said.
Over the course of the study, the researchers found that the initial dose led to a rise in antibodies over the first 6 months, followed by tapering of levels at 12 months. In the next year, antibody levels stabilized at 10 to 20 times higher than baseline levels, reflecting a “robust immune memory despite the 2-year delayed interval of boosting,” Sahasrabuddhe said.
He said that although the results also suggest that deferring a booster shot for 2 years could be acceptable, it is crucial to continue following CDC guidelines.
“The CDC still recommends that children aged 11 to 12 get a two-dose series of the HPV vaccine, 6 to 12 months apart, starting as early as age 9,” Sahasrabuddhe said. “It is therefore important to continue following CDC guidelines on HPV vaccination dosing and schedules.”
Although the results are “encouraging,” Sahasrabuddhe said, longer term data are still needed to evaluate immune responses over 2 years.
“Several studies to answer these questions are underway,” Sahasrabuddhe said. “The NCI is supporting a large, randomized double-blinded trial of more than 20,000 girls in Costa Rica to test testing whether one-dose HPV vaccination is as effective as two doses at preventing persistent HPV infection, as a surrogate of cervical cancer risk. Results of the Costa Rica trial are expected in 2025.”
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