Real-World Effectiveness of Human Papillomavirus Vaccination Against Cervical Cancer

Abstract

Background: The primary goal of human papillomavirus (HPV) vaccination is to reduce morbidity and mortality from HPV-associated disease, especially cervical cancer. We determined the real-world effectiveness of HPV vaccination against cervical cancer.

Methods: The study included women aged 17-30 years living in Denmark October 2006-December 2019. From nationwide registries, information on HPV vaccination and cervical cancer diagnoses were retrieved. Incidence rate ratios (IRRs) with 95% confidence intervals (CIs) for cervical cancer according to vaccination status were estimated using Poisson regression with HPV vaccination treated as a time-varying variable and stratified by age at vaccination. We adjusted for attained age, education, and ethnicity. To address the effect of prevalent disease, different buffer periods were used, with 1-year buffer period as primary analysis.

Results: The cohort comprised 867 689 women. At baseline, 36.3% were vaccinated at age 16 years and younger, and during follow-up, 19.3% and 2.3% were vaccinated at ages 17-19 years and 20-30 years, respectively. For women vaccinated at ages 16 years and younger or 17-19 years, the IRRs of cervical cancer were 0.14 (95% CI = 0.04 to 0.53) and 0.32 (95% CI = 0.08 to 1.28), respectively, compared with unvaccinated women. In women aged 20-30 years at vaccination, the incidence rate was higher than among unvaccinated women (IRR = 1.19, 95% CI = 0.80 to 1.79) but slightly decreased with increasing buffer period (IRR = 0.85, 95% CI = 0.55 to 1.32, with 4-year buffer period).

Conclusion: HPV vaccine effectiveness against cervical cancer at the population level is high among girls vaccinated younger than age 20 years. The lack of immediate effect in women vaccinated at age 20-30 years points to the importance of early age at vaccination.

Figure 1.

Cumulative incidence of cervical cancer by attained age and stratified by age at vaccination. Analyses are shown for women vaccinated (A) age 16 years or younger, (B) 17-19 years, and (C) 20-30 years.

Figure 2.

Incidence rate ratios (IRRs) of cervical cancer comparing vaccinated with unvaccinated women by length of buffer period and stratified by age at vaccination. Analyses are shown by age at vaccination for (A) age ≤16 years or younger, (B) age 17-19 years, and (C) age 20-30 years. Error bars indicate 95% confidence intervals.