After the introduction of a national human papillomavirus (HPV) immunization program in England, there was a significant decrease in cervical cancer diagnoses and incidence of grade 3 cervical intraepithelial neoplasia (CIN3) in young women, according to results of a study published in The Lancet.
In this observational study, researchers employed an extension of the age-period-cohort Poisson model to estimate the relative risk reduction (RRR) for cervical cancer rates among 3 cohorts (cohorts 5-7) of adult women aged 20 to 29 years who received the HPV vaccine compared with 4 cohorts (cohorts 1-4) of those who were not eligible for vaccination. Researchers used data from a population-based cancer registry to assess cervical cancer diagnoses and incident CIN3 among women aged 20 to 64 years between Jan 2006 and June 2019. The researchers enrolled participants into 3 cohorts stratified by age to account for differences in the school year in which the HPV vaccine was offered and its national coverage. In addition, adjustments for confounding factors were made by analyzing information on changes in cervical screening policy and historical events that affected the incidence of cervical cancer.
Participants in cohorts 5, 6, and 7 were offered the HPV vaccine between school years 12 and 13, 10 and 11, and in year 8, respectively. The researchers analyzed data from a total of 13.7 million follow-up years. Compared with participants in the unvaccinated reference cohorts, the researchers found that the estimated RRR in cervical cancer rates following HPV vaccination were decreased by 34% (95% CI 25-41) among those in cohort 5, 62% (95% CI 52-71) among those in cohort 6, and 87% (95% CI 72-94) among those in cohort 7. In regard to incident CIN3, the researchers observed an RRR of 39% (95% CI, 36-41), 75% (95% CI, 72-77), and 97% (95% CI, 96-98) among participants in cohorts 5, 6, and 7, respectively.
Similar results were obtained across models with adjustments for confounders. By June 2019, it was estimated that there were 448 (95% CI, 339-556) fewer than expected cervical cancer diagnoses and 17,235 (95% CI, 15,919-18,552) fewer than expected incidences of CIN3 among participants in the 3 vaccinated cohorts.
This study was limited by its observational design, the inability to assess the efficacy of the vaccine due to the lack of individual-level data on vaccination status and HPV type, and its small sample of vaccinated participants expected to develop cervical cancer in the absence of vaccination.
According to the researchers, “our findings add evidence to the very limited literature showing that national HPV [immunization programs] can lead to a substantial reduction in cervical cancer incidence, especially if vaccination coverage is high and women are offered the vaccine at a younger age.”
Falcaro M, Castañon A, Ndlela B, et al. The effects of the national HPV vaccination programme in England, UK, on cervical cancer and grade 3 cervical intraepithelial neoplasia incidence: a register-based observational study. Lancet. Published online November 3, 2021. doi: 10.1016/S0140-6736(21)02178-4