HPV Vaccination Provides Sustained, Long-Term Protection Against Cervical Cancer
A study published in The BMJ indicates that human papillomavirus (HPV) vaccination is associated with a significantly reduced risk of invasive cervical cancer, with no indication of waning protection for up to 18 years after vaccination.
Study Background
HPV is a common sexually transmitted infection. Many countries utilize vaccination to protect individuals, primarily girls, against cervical cancer and other related cancers. However, data on the long-term durability of vaccine protection and potential differences based on age at vaccination have been limited.
Methodology: An 18-Year Nationwide Follow-Up
Researchers in Sweden conducted an 18-year follow-up study, spanning from January 1, 2006, to December 31, 2023. This comprehensive study utilized nationwide registers.
The study cohort included 926,362 girls and women born between 1985 and 2001. Crucially, none of these participants had previous HPV vaccination or a diagnosis of invasive cervical cancer at the start of the follow-up period.
Participants were followed up to a maximum age of 38, with those vaccinated before age 17 followed up to age 34. The analysis meticulously adjusted for various factors including age, county of residence, mother's country of birth, history of high-grade cervical lesions and non-cervical cancers, and parental education and income.
Key Findings: Sustained Protection Across Age Groups
During the follow-up, 365,502 (40%) participants received at least one dose of the quadrivalent HPV vaccine. A total of 930 cases of invasive cervical cancer were identified, with 97 in vaccinated individuals and 833 in unvaccinated individuals.
Early Vaccination: Significant and Lasting Protection
Individuals vaccinated before age 17 experienced a remarkable 79% lower risk of cervical cancer compared to the unvaccinated group. This protection remained sustained, with a 77% lower risk observed 13-15 years post-vaccination, demonstrating no indication of waning effectiveness.
Later Vaccination: Emerging Long-Term Benefits
For those vaccinated at age 17 or older, a 37% lower risk of invasive cervical cancer was observed compared to the unvaccinated group. Interestingly, this protection increased over time for this group. A 46% lower risk was observed 10-12 years after vaccination, further improving to a 77% lower risk 13-15 years after vaccination.
Population-Level Impact
The study also noted a significant population-level decrease in cervical cancer cases over time. The rate was highest in women born between 1985 and 1988 (around 250 cases per 100,000 by age 38). This rate progressively decreased for younger birth cohorts. For women born between 1999 and 2001, the rate was significantly lower at 4 per 100,000 by age 24.
Important Considerations: Acknowledged Limitations
As an observational study, the authors acknowledge potential limitations. These include possible misclassification of some vaccinated women as unvaccinated. They also recognize the possibility of a healthy volunteer bias and that unmeasured factors, such as smoking and sexual activity, may have influenced the results.
Conclusion: Strong Evidence for Global Elimination Strategies
Despite the limitations, the study's large scale and use of high-quality, nationwide data suggest the findings are robust.
The researchers conclude that the study provides evidence of sustained protection against invasive cervical cancer for 18 years, with no indication of waning protection.
These findings strongly support global strategies aimed at eliminating cervical cancer as a public health problem through high-coverage routine HPV vaccination, particularly in younger populations.