Reduced Risk of Cervical Lesions Among Girls and Women 6 Years After Licensure of HPV Vaccine in Denmark
In a cohort study reported in the Journal of the National Cancer Institute, Baldur-Felskov et al found that there has been a significant reduction in cervical lesions among Danish girls and women receiving the quadrivalent human papillomavirus (HPV) vaccine during the first 6 years of its availability.
Study Details
In the study, all girls and women born in Denmark in the period 1989 to 1999 were identified, information on individual HPV vaccination status in the period from 2006 to 2012 was collected from nationwide registries, and incident cases of cervical lesions were identified by linkage to the nationwide Pathology Data Bank. Frequencies of lesions were compared for vaccinated and unvaccinated girls and women stratified by birth cohort in Cox proportional hazards models.
By birth cohort, total population and number of vaccines were 78,448 and 11,243 (14%) for 1989 to 1990, 74,323 and 19,867 (27%) for 1991 to 1992, 72,544 and 63,922 (88%) for 1993 to 1994, 71,214 and 63,912 (90%) for 1995 to 1996, and 102,715 and 88,369 (86%) for 1997 to 1999.
Risk Reductions
For the 1989 to 1990 cohort, vaccination was associated with a significant reduction in risk of lesions categorized as atypia or worse (hazard ratio [HR] = 0.75, P < .001) and nonsignificant reduction in risk for cervical intraepithelial neoplasia grade 2 or 3 (CIN2/3; HR = 0.88, P = .32) and CIN3 (HR = 0.78, P = .20). For the 1991 to 1992 cohort, vaccination was associated with significant reduction in risk for atypia or worse (HR = 0.46, P < .001) and CIN2/3 (HR = 0.56, P = .005) and a nonsignificant reduction for CIN3 (HR = 0.64, P = .13).
For the 1993 to 1994 cohort, there was a significant reduction in risk for atypia or worse (HR = 0.40, P < .001), CIN2/3 (HR = 0.27, P = .005), and CIN3 (HR = 0.20, P = .01). For the 1995 to 1996 cohort, there was a borderline significant reduction in risk for atypia or worse (HR = 0.43, P = .08). There were too few events in the 1995 to 1996 cohort to permit calculation of hazard ratios for CIN2/3 or CIN3, and there were no events in the 1997 to 1999 cohort.
The investigators concluded, “Six years after licensure of the quadrivalent HPV vaccine in Denmark, a reduced risk of cervical lesions is observed at the population level.”
Susanne Krüger Kjaer, MD, of the Danish Cancer Society Research Center, is the corresponding author for the Journal of the National Cancer Institute article.
The study was supported by the Mermaid project (MERMAID 2). For full disclosures of the study authors, visit jnci.oxfordjournals.org.
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