A landmark 17-year study published in JAMA Pediatrics has demonstrated that human papillomavirus (HPV) vaccines provide exceptional protection against cervical cancer-causing infections in real-world community settings, benefiting both vaccinated and unvaccinated women through herd immunity effects.
The research, led by Dr. Jessica Kahn from Albert Einstein College of Medicine, followed 2,335 adolescent and young adult women in Cincinnati from 2006 to 2023, spanning the period from just before the first HPV vaccine became available through widespread implementation.
Dramatic Infection Rate Reductions Among Vaccinated Women
The study revealed striking effectiveness rates across different HPV vaccine formulations. Among vaccinated participants, infections from HPV types covered by the 2-valent vaccine fell by 98.4%, while infections from types covered by the 4-valent vaccine dropped by 94.2%. Even the more recently introduced 9-valent vaccine showed a 75.7% decline in targeted infections.
"HPV vaccines work remarkably well in a real-world setting, even among women at high risk for HPV and who may not have received all vaccine doses," said Dr. Kahn, professor of pediatrics and the Dr. Ernest Baden Chair in Head and Neck Pathology at Einstein.
The study population represented a higher-risk demographic than typical clinical trial participants, with 79% reporting two or more male sexual partners and 51% having a history of at least one sexually transmitted infection. Participants ranged in age from 13 to 26 at enrollment and were considered vaccinated if they had received at least one dose of any available HPV vaccine.
Strong Evidence of Herd Immunity Protection
Perhaps most significantly, the research documented substantial protection for unvaccinated women through herd immunity effects. Among unvaccinated participants, infections with HPV types covered by the 2-valent vaccine decreased by 71.6%, while infections with types covered by the 4-valent vaccine dropped by 75.8%.
"We saw clear evidence of herd immunity, meaning when enough people are vaccinated, the vaccine indirectly protects unvaccinated people by reducing overall virus transmission," Dr. Kahn explained. The high degree of herd immunity was likely related to robust vaccination rates and vaccination of both boys and girls.
Global Health Implications
HPV represents a significant global health burden, serving as the most common sexually transmitted infection worldwide and the primary cause of cervical cancer. According to the International Agency for Research on Cancer, HPV is responsible for more than 690,000 new cancer cases annually, representing about 4.5% of all cancers globally.
The study's findings carry particular importance given current global vaccination disparities. While vaccination rates in the study population increased from 0% to 82% over the 17-year period, globally only 27% of girls have received at least one dose of HPV vaccine, with coverage ranging from just 1% in the Eastern Mediterranean region to 68% in the Americas.
Real-World Validation of Clinical Trial Data
The research addressed a critical gap in understanding HPV vaccine effectiveness outside controlled clinical trial settings. "Participants in those studies tended to be healthier and at lower risk for HPV than the general population, so they weren't necessarily representative of the broader community," noted Dr. Kahn, who also serves as senior associate dean for clinical and translational research at Einstein and Montefiore.
First author Aislinn DeSieghardt, clinical research coordinator at Cincinnati Children's Hospital Medical Center, emphasized that the analysis indicated infection rate reductions were primarily due to vaccine introduction rather than changes in sexual behavior or other factors.
Path Toward Cervical Cancer Elimination
The study results support optimistic projections for cervical cancer prevention. "In the U.S. and other countries with widespread HPV vaccination programs, cervical cancer rates are already declining," Dr. Kahn observed. "By expanding uptake of this highly safe and effective vaccine, and ensuring access to screening and treatment, we can achieve one of the greatest public health victories of our time: the elimination of cervical cancer worldwide."
The research encompassed three generations of HPV vaccines: the 2-valent vaccine protecting against HPV types 16 and 18 (responsible for over 70% of cervical cancers), the 4-valent vaccine adding protection against types 6 and 11 (causing about 90% of genital warts), and the current 9-valent vaccine introduced in 2014, which targets nine HPV types responsible for about 90% of cervical cancers.
